There can be much done to shove crit-bursters in the ground, that's the problem. Simply trying too hard, too much to change at once can just ruin them completely, i advise simple changes at first, then observe the results.
My " wild " guess is to cut down existing damage multipliers for about 1/5( if 90-80 roll 4x multiplier, then set it to 3.2x, if 80-70 roll 3.5x, change it to 2,8x, this is not only going to make the overall damage of critical hits lower, but make their damage a little bit more consistent?, instead of 0.5x difference between rolls, it's gonna be 0.4x ) well obvious, nerf the damage. Isn't RL doing some mad 200 criticals already? If that's so, with the AOE ability it wouldn't be bad to nerf a bit.
Then the bypass problem, it's not game breaking for a sniper to do regular bypasses due to their mechanics, how they work, flaws, advantages etc. etc. their well balanced, skill based. Though for a big gunner, i don't think they should be possible to do regular bypasses, currently even against 5 luck characters it results roughly for about 30+% chance to score a bypass, that's god awful too much if you ask me. Cut down it by at least 1/3 for sure, instead of 60% on 1 luck, that's gonna be 40%, dooh.
Perks, armor, frequency of critical hits, weapons, nothing else is not touched at all.
After this, we could " test " and provide some feedback and insight, maybe something else will need to be attacked, maybe this will do the trick.