If you want to win at submission only, you must use the shortest pathways to submissions.
Generally this means, attacking leg entanglements, attacking guillotine chokes, and attacking ezekiel chokes, with honorable mention to attacking the back.
Most forms of passing really are an only tangentially useful skill in sub only, where if most relevant would be in situations like combination sub/pass positions (like front headlocks and double wrist locks), or in rescuing yourself from poor leg entanglement position (
like berimbolo-counter rolling back takes off slx or saddle,
or crab ride back takes off double outside ashi), or in escaping submissions (like
triangle chokes or
armbars).
Training time and recovery are limited resources; one must think hard about whether a particular wrinkle is really adding value, and not taking away from essentials that are truly vital to the competition; sub defense and 2 or 3 A-game sub attacks. (There is no shortage of highly talented grapplers, with years of experience, getting heel hooked within minutes in sub only comps).
When approaching a buttflopping opponent in sit-up guard posture, particularly wrt an opponent looking to use leg entanglements, the first option of course is to be even better at leg entanglements than he is.
If your tastes happen to lie more in asymmetry, then, the next primary method of attack is head chanceries. If sat up/hunched, you go to the cow catcher/arm weave, and if he lets you roll him back, you go to the ezekiel.
In any case, one must have a specialized A game with a golden hammer to get stoppages against top competition, but each also of the matters mentioned heretofore are valuable to be at least proficient in as well. Since you also fight mma, head chancery attacks will likely have greater overlap with your expected use-cases.
Para exemple:
Regarding your first match, attacking closed guard is an underserved and valuable strategy in sub only as pinning your opponent in closed denies him access to your legs. In both matches in fact it would've been a low risk strategy simply by going to the ezekiel until it sinks. If for whatever reason you simply must pass (such as escaping the rubber guard), the tozi pass is a preferable option here, as it again maintains the pin.
The guy with the best ezekiels in the game in my opinion is Braulio Estima, so if you happen to have a subscription to estima in action you're in luck (he has good details on tozi passing as well [though he calls it the 'sao paulo stack']).
Excepting that this the closest video i've found so far that resembles to the way he does it (the main difference is that he lifts the head with the head wrapping arm, pushing their neck into your hand, rather than just pushing your hand into their neck alone, which lets you put more weight and torque into it).
Besides the regular no arm attack there are in fact several variations of chokes you can use to attack the guard (or mount); for instance 'arm in ezekiels' (or 'front nelsons' if you will) are also an option for greater control.
(bonus vid just because)
In your second match, your opponent used collar ties often, which gives the opportunity for slide-bys to merkel/seat belt. When you have the underhook you should drive in at a more oblique critical angle, looking to throw him by, making it harder for him to pull you over with the donkey kick. When you were in over/under and he lateral dropped you, you should step to the other side (your overhook side) to hit the knee tap or metzger/ko soto gaki.
The instinct to pull away from the guillotine in guard basically helps him finish it easier. You want to go into him and post on your head, which takes away a lot of his torque, allowing you to survive in the position. See for example Woodley's unsuccessful choke attempt on Thompson. Next, you want to swim your hand over his head while twisting the hips in, transitioning into the tozi break.
As always make sure your balance, posture, and pressure, is on point so he doesn't sweep you over and pin you with a mounted guillotine, which is basically game over and always the ultimate goal when you yourself are attacking with front headlocks.
