Would a different pistol have mattered? If not, it's irrelevant. For a duty pistol, the ability to not shoot when you don't want to is a huge consideration. Everyone draws a lot more often then they shoot, and cops point a lot more than they shoot. Hence things like DAK and LEM that aren't the most shootable triggers but help manage risk in no-shoots.
I'm not a big fan of never and always. I was able to set my feet and lean into my gun several times during my real gun fight. Sure, sometimes it was modified to roll out from behind cover, sometimes I was on the move, but when I set and fired at the end I was exactly how I trained on the square range. I won't say it mattered. Maybe I could have been balancing on one foot and had the same results.
I *think* it was @Mas who told me this, but I can't recall 100%. The "t-rex arm" posture simulates a specific injury to your arm so that your bicep has contracted due to the lack of resistance after your upper arm bone has been broken. You can still close your fist but can't uncurl your arm. Latching on to your own clothing helps stop the arm from swinging around upsetting your balance, etc.
It's definitely proven that tightening your off hand helps your strong hand grip tighter simultaneously. I don't recall the name for why, but it's got to do with the way the nerves tell the muscles to fire.