Oh I agree with you on this. However.... If I'm hitting you 10x harder, do you think accuracy of finding those little chinks in your armor is really going to matter a whole lot? I'm going to hit you and you are going to feel it.
Also barbarians, aka berzerkers fight normally in an un thinking random style. A season veteran who is used to formality and training can be taken aback by this shere randomness and unwittingly leave openings when normally there would be none.
Note, I'm not advocating for or against the current implementation. I'm just giving you another way to look at it. Either way, raging should increase damage (which it does). Remove the current crit enhancement and you have to replace it with something else. (I currently doubt they'll take it away, unlike evasion in full plate that I knew they would.)
Lessening the time on exhaustion is not the way to go as eventually barbs will get tireless rage.
Improving the crit range has been shown as unbalancing. Well.. the op is suggesting to increase the crit multiplier instead. Apparently the tech has been added for this if I've read the dev notes correctly.
However, There is another suggestion. Change the while raging stat enhancements. Instead of just a +1 str/con bonus, you could always make them go up by +2 per increment instead at the same cost. While powerful, it is not as over powering as the crit range is. Just another idea to toss into the fire.