I'm not aware of 'abrams armour'
Advanced Power Armor MK-II
18 hp / 60%
20 hp / 70%
19 hp / 90%
18 hp / 60%
16 hp / 70%
50 lbs
AC 35 (armour class)
the HP stats define the minimum damage that must be done before the user takes any damage,
the damage done is altered by the % reduction.
thus, in advanced PA km2 no, you wouldn't feel a rock being thrown at you, and I can agree that in this situation that the idea a 'super-crit' can essentially bypass all that is a little silly, but as far as I'm aware a rock cannot obtain a ridiculous crit.
However, weapons such as lasers, mini-guns, plasma rockets and flamers CAN cause massive crit's (along with burst fire from most burst capable weapons)
In the situation where the attacker opens fire with a mini-gun and its 100 rounds per second (imagine 100 bullets.. then imagine them heading toward you VERY fast ... ) and those bullets for some unforeseen reason find the gap at the knee, or groin or neck (power armour unlike tanks has to have greater mobility) your sure as hell gonna notice those 100 or so bullets making their way through that weak point and then ripping up whatever was behind the armour plating.
So, rick Vs, tank this is not, we are mostly talking highly destructive weapons Vs a VERY old suit of mobile armour
Overall I still stand by the idea of massive crit's, and if you don't want to risk being blown apart by them, don't engage enemies with weapons likely to do so. perhaps try 'sneaking' instead of balls to the wall gun-play?
don't like saving, you don't HAVE to hit F5 every 5 mins.. play an ironman game (i.e only save when your about to exit the game / sleep) and when the character dies, he's dead. That's how life in the wastes should be!
small post-post edit
regarding your comments about AI tactics, dont forget, the original FO games are quite aged now. Only now in modern (and often only in 'mil-sim' games) do we see combat aware AI models. And in some defence in Fallout Tactics, I cant recall the amount of times I was facing opponents that refused to budge from behind sandbags or in a trench, forcing me to use alternative assault tactics (as I knew running toward them I'd suffer serious damage OR shock horror... a super crit!) I'll agree that FO 1/2 had limited AI, but lets face it, FO3 the enemy actually insist on running toward you, in the open, firing until either you or they are dead (usually them) so it hardly a part of 'terrible old game AI programming'
If you want games with enhanced AI, I'm sorry to say you'll have to look further than FO 1/2, but there are games out there that do have this as a feature.