Have to disagree...
First I often wait to fire my big ship, instead firing ships that are in danger of blowing up if not fired right awas.
Second its not just the 4-6, that particular crit is truely worse than others only on the second (or with most big ships third to fifth) turn when your in the middle of the brawl. The two lose an arc ones are just as bad (if its your bore/front), as is the no movement one for boresighters, or the 4+ to fire one half the time. And after one experience with a triple damage weapon hitting an Avioki and blowing it up in one shot...well there you go, sounds like a large part of the crit chart can be an issue.
As to the reverse defeating the purpose of crits in the first place, that not accurate. This system does not remove crits from the game as a concept, it slows their effect on large ships by frankly a minimal amount. It buys you a turn maybe two for the really big boys, if you are under any concentrated fire. And as you say how often do you not concentrate fire on the enemy big boys? (I am being sarcastic here as there are good reasons to go for small fry first.)
Not saying there are not issues with the idea...specifically races that depend on not being hit benefit more, precise races suffer some, etc.
Ripple