The only thing that makes sense to me is to figure out a way to allow strikers to create angles to attack around or through the guard. I know I'm in the minority here but I don't think holding block should drain stamina. At least not in an absolute sense.
Now, to some of the other points you made: clinch Grappling, wrestling, jiu jitsu, scrambles, AND damage from blocking strikes should absolutely affect 'arm stamina.' Different from holding hands up draining general stamina. Does that make sense? And weak/tired/beat up arms should have repercussions, as explained in previous posts in this thread.
Haz, you do make a great point though, and I don't think it's emphasized enough in the current game. If you hold high block you should have a super hard time stopping a takedown (if done from a decent distance etc.). The reason we learn to fight with a different stance from boxers is precisely because of the takedown element. You have to be ready to get underhooks to stop the shot. Same goes for overreaching with the lead arm and getting over that front foot -- again, easy takedown.
Just pointing out some things that are simple to implement in the game as counters for this stuff. I do admit, aside from easier takedowns and a wide open body, I struggle to think of a good way to deter this... (one idea just popped into my head though: high guard held constant means no elbow to deflect body blows - perhaps liver shots should be implemented into the game. Step left and kick/punch a clean liver shot from the perfect distance means game over, no more eating 20 clean body kicks in a fight. That will change behavior)