I agree, and the jump between +2 and +5, is, itself, a pretty big deal. Even when imps have a critter, assuming you want to specifically run up a class just for access to that crew member, they don't have it at as high a quality. Smuggler, trooper, and jedi knight dominate the options for armor, biochem, and arms.
This is that old routine of the game bonus question where you offer a player +30% xp, or a 1% extra damage. It sounds like you want the xp while you level, but you're going to be cap someday, and the efficiency improvement won't matter to you anymore--all you will want is access to better stats which you can't get any other way than RNG and luck.
Maybe they should just put crit into companion opinion of you and give them base efficiency improvements. They simply classify a companion as 'talented: cybertech' or whatever. That way they can do a behind-the-scenes calculation to crit, regardless (which they can also balance whenever they feel like universally across companions), and give a uniform speed bonus in the chosen discipline.
So for example: 4X; talented (Cybertech). His crafting comes out 15% faster, from word go, but as you get him more affectionate, behind the scenes he gains an extra cybertech crit bonus. Which helps him make awesome droid parts. Which nobody cares about and won't buy on the GM. But good for him--he should have a hobby.
This isn't a bad suggestion, but I think it should still be at different levels if this was done. Say, 4X only giving a +5% efficiency and +1% crit for cybertech, while giving a +15% efficiency and +5 crit for scavenging. Not that I dislike the current system, but I could work with your idea too.