I've house ruled that FOREVER. More damage should matter. Unless I run a game that is meant for beginners or strict tournament rules I used that rule. I think it is in Tac Ops.
There is a "stacking 20's" rule in TacOps that adds +1 to the PSR for every 20 points the unit takes, BUT, the other half of the rule that is often forgotten about/overlooked is that the PSR is also modified by the weight class of the unit making the PSR.
L = +1,
M = 0,
H = -1, and
A = -2)
So, if you're using the stacking 20's rule and your Atlas takes 40+ points of damage in a turn, he's going to make a PSR with a +2 penalty (for the stacking 20's) and a -2 bonus (for being an assault mech).
At the end of the day, IMO, the use of the full stacking 20's rule unfairly reduces the value of a light mech without actually reflecting it in BV2.