To give helpful actual advice, the best thing to have is actual footage!
First things, its a good look getting after it right away with an aggressive shot like that on reaction; always remember what your strongest weapons are and specialize your training around them, as those are what will give you a weapon strong enough to threaten elite competition, whereas over-generalization might leave you with a plethora of avenues that are all equally just short of good enough.
The single leg to SLX in particular is an effective tactic even against opponents with very strong take down defense, as Paul Harris repeatedly demonstrated throughout his fractious (and fracturing) career.
However, there are some problems with the positioning and breaking mechanics, which allowed your opponent to escape without concession.
To begin with, more optimal controls from the anaconda/ashi situation comes from either, placing your foot on his hip and connecting your other knee to it, clamping down and pinning his trapped thigh, or pushing your foot deep across to dig under his far thigh. Having your leg flailing out in space across his body like that affords little control or mechanical advantage.
Second is the question of breaking mechanics. Here you are committing the classic journeyman mistake of trying to finish the heelhook by pulling it across the body. This is suboptimal in terms of anatomical pressure, and in fact can actually help him escape easier on top of that. Rather than pulling across, you pull it tight and
screw it in, which allows you to bring more force to bear while also keeping him stuck.
Here are some illustrations of these principles.
The next sequence involves more of a personal opinion of mine; i don't actually think the arm bar is that great of a technique, and that the double wrist lock position (with the keylock or chickenwing finish) is superior in pretty much every way; more control, more versatility, and more reliable finish.
Now, the more general issue at play in this part is something that a lot of BJJ fighters transitioning to MMA have difficulty with. Which is, insufficient skill at riding the opponent and keeping him pinned.
There's a good saying on the subject that i call the 'Schalles Principle', which is: Kill first, Pin second.
In collegiate wrestling, pinning your opponents shoulder blades to the mat is total victory, ending the match. More than this, in dual meets, pinning your opponent gives your team
bonus points in the count towards which team wins the meet. Hence, if an athlete ever feels like he is in any danger of getting pinned, he is going to fight like hell and do everything in his power to
not get pinned, making it rather difficult to actually pin him. Thus, if Mr. Schalles wanted to consistently finish his opponents, he would have to
convince them, to
accept being pinned. Ergo, he has to kill them.
Extrapolating, it is just the same when attempting to attain a submission hold over a determined opponent, thus: Kill first, Submit second.
So it goes; tis not a question of position or submission, but having your
position itself be a submission. Using your ride to apply pressure to vulnerable areas, to steal his breath, constrict his blood, and burn his energy as he futilely attempts to escape.
After all, the easiest way to choke someone out in under 10 seconds, is to have
already been choking him out the other 170 seconds too.
Something else to note is how, too often when watching good grapplers in mma, you see them maybe take someone down, get on top, do lots of cool looking things like passing, taking mount, and what not... and then the bell rings. What do you know, up comes the start of the next round, and they look dead on their feet while their opponent has a spring in their step, promptly K-ing them TFO.
The reason is, simply, that they failed to
punish their opponents sufficiently when on top, when they had the opportunity. If you want to be on the positive side of the energy differential function, you must learn to punish your opponent; you must learn to give him the presh.
From side control, there are triune implements of pinning, punishing, and finishing. The strongest and most versatile in my view, is the nelson hold.
There are many examples
Two others you may situationally find yourself in are the reverse seatbelt/reverse nelson, and the head-and-arm/scarfhold. Of course it pays for one to presume to provide the presh in these particulars as well.
The subsequent difficulty in this performance is a mirror of the previous one; insufficient skill in
escaping your
opponents riding.
Felicitously, both problems can be elegantly solved at once in training a team, as drills for holding your opponent down are the same as drills to escape your opponents hold downs.
When you are on bottom in MMA, you want to be either clinching and
taking all the space, or pushing away and
creating all the space. The limbo inbetween is optimal striking range, which of course greatly favors whoever is on top; you, or your opponent.
This usually means some variation of butterfly guard, to dive under for legs, or push off to stand up. It can also some some form of clinch like rubber guard/rat guard/williams guard. 'Regular' closed guard does not have much space in this schema, as it is a situation where your opponent is pinning you, yet at the same time your control over his attacks is limited.
Of the classic closed guard 'big 3', the coil lock/omoplata situation is a major exception. Since, even if you don't actually use it to finish, it creates space that allows you to escape, or transition to the more dominant double wrist lock situation, especially from the leg hook/lister grip.
Some example fights that show effective escapes against a dangerous opponent would be, Moussasi vs Weidman, Aldo vs Edgar and Mendes I-II, Macdonald vs Maia, Maia vs Nelson, Lawler vs Macdonald, Lawler vs Hendricks, Werdum vs Silva, and GSP vs Fitch.
On the subject of your side choke/arm triangle, we will skim over the topic, as the previous section on pressure covers most of ones use-cases in such situations anyways.
We will note however, that whether clinched against the cage, inside your opponents guard, or sitting in mount, the no-gi ezequiel is a highly versatile and effective move. With devoted training time to proficiency, passing simply for passing's sake can become almost an after thought, as you are always mere moments away from a finish whenever on top, as Alexey Oleynik has demonstrated repeatedly.
A related option is the square choke/box lock, which, like the ezekiel is applicable with dominant clinch position, is also applicable when tripoding, tozi passing, or really any other time one is using head pressure.
Finally, we must have a final solution for the GnP question.
Simply put, your ground and pound, quite frankly, sucks. You're huffing and puffing flailing your arms around willy nilly, yet at the same time were barely even touching him, and then you're looking at the ref as if he is gona stop anything on account of some spastic game of patty cake. Just awful, just plain awful.
Luckily, there is One Weird Trick that can take someones gnp to the next level, and that is, HAND CONTROL.
Hand control does many things for one; chief among them the fact that, regardless of whatever their special particular game may be which you may or may not be aware of, you can bet that he will find it especially difficult, if not impossible, to actually get it going without control of his limbs.
Even better, and more pertinent to the ground and pound situation, is the fact that with hand control one can pin the hands while posting up and making frames, whereupon you can then drop hellbows on their unprotected face while they are trapped. High impact, high
efficiency ground and pound.
Especially related to hand control is the gift wrap situation, which is always a good grip to work towards, as it opens up both strikes *and* super strong chokes such as giftwrap arm triangle or giftwrap ezekiel.
And of course, there is also the most dominant ground and pound position of all: the side control/mounted crucifix.
Few fighters have put in the time to master this transition, but those that have, are overwhelming threats on top, championship level threats; men such as Matt Hughes, Demetrious Johnson, or Khabib Nurmagomedov.
As a last word, we must mention conditioning. Specifically, the lack of it.
Fatigue makes cowards out of all men, it is something that
everything else is contingent upon; no matter what skill, what talent, what ability you have, it all goes away when the gas starts running out.
It could be your aerobic capacity, it could be that you're overly tense, it could be that your movement engrams lack polish and efficiency. Very likely, it is a mixture of all three. In any case, they are all things vitally necessary to work on in training; endurance is by far the most important somatic attribute to success in combat, in near all its forms.
Hope this helps!
