One other thing you might consider is rather than going to half, try going to butterfly.
For instance, at 2:15 of your no-gi match with the big guy, you might have inserted your left hook rather than going to halfguard (with some Z guard mixed in). Although you eventually recovered full guard, there were two minutes of squishing and near-passing that looked painfully familiar to my experience.
I played a ton of halfguard for about two years, mainly because my instructor at that time was a halfguard specialist (Lucas Leite style).
Now, I also tried a lot of butterfly at times, but always got destroyed because I tried to use the Marcelo style (like in his book). I characterize this style as being square to the opponent, having fantastic grip fighting skills (I didn't), and being able to scoot in under the opponent's center of gravity quickly and trigger the sweep quickly using treetrunk legs (which I didn't have). This Marcelo style did not favor my build, speed, grip-fighting ability, attributes, or the large size of many of my training partners. This is no knock on Marcelo of course, just my poor interpretation of his techniques.
Meanwhile, the halfguard worked OK with no-gi smaller guys, but in the gi and with big guys, even if I got the sweep or took the back, I was exhausted and it looked a lot like what you went through from 2:15-4:15 of your video 2.
About 9-12 months ago, I started playing more of the Carlos Machado style hookflip. This is better than the Marcelo style for people like me (weak and slow). I was training a lot at that point with an instructor that trained up through purple with Carlos, and he understood how to make it more safe, no squishing with lots of strong frames and angles.
Several months ago, I got the Carlos Machado Unstoppable hookflip DVD and since then, it's become my best style of guard. The grip he uses at :39 of the preview works great with big guys in no-gi:
Budovideos.com - Unstoppable: Secrets of the Hook Flip DVD with Carlos Machado
I can't recommend it highly enough. I can now easily flip guys 100 lbs heavier than me, as well as quick and technical guys. There are a lot of holes in my hookflip of course, but at least I'm not suffering all the time like I did with getting squished in the halfguard or the Marcelo butterfly.
Probably more suggestions and personal anecdotes than you wanted to hear. I want to say most of all I admire you competing and sharing your footage, you looked tough as nails!