We could certainly quibble over details here, but even if we assume this was embraced at every table and implemented as you say, I think it doesn't come close to approaching the balance issues you find in 3E with class dipping and feat combos. Two weapon fighting was a known issue in the game, like specializing in darts. It was pretty easy to work around or just accept. At the time, everyone wanted to be a twin blade wielding loner because of the drizzt books. But to be honest, i didn't see it that much in groups after the first year or so. With the complete books you have a lot of optional rules that are very much an "incorprate at your own risk" type of thing, plus some questionable changes (like extending specialization to paladins and rangers). But the kits were so easy to control. Most just gave you NWPs and circumstantial bonuses. Those that were busted you simply didn't allow. But kits were something you layered on your class, they were not like the prestige classes or new classes in thelater complete books, where you had players combining them to really unexpected results. With 2E the balance issues that existed were known, there just wasn't that level of surprise you bumped into again and again in 3E (and i do like 3E, it just has more balance issues to juggle).
Another key difference between the 2E complete books and 3E complete books is the ratio of flavor to crunch. The 2E books offered some mechanics, but the kit entries were mainly about character ideas and text explaining the concept. That is why the complete Bard was so popular and still highly regarded among 2E players. No one really cares about the kit bonuses, they like it because it has all kinds of useful infomation about bards and being a Bard. Heck, if you are only going to buy one complete book for 2E, it should be the Bard book IMO because it can add a lot to the game.
I have been useing the 2E system for time again, including the class complete books. It has been way easier to manage than 3E in terms of balance. 3E has lots of advantages though. It is a lot more customizeable. So when I did my wuxia campaign, i used third edition because it was was a btter fit for the genre and had way more mechanical options for turning martial characters into wanderin martial heroes like you see in the Condor series.
I am in no way saying 2E is perfect. It isn't. And 4e is definitely more balanced than 3E or 2E, but 2E is pretty well balanced and still gives me a lot of what I want. The kind of balance achieved in 4E just isn't what I am looking for. I find between 2E and 3E (and occassionally 1E) I can get what I need for a gameof D&D. I go to 3E for its flexibility and unified mechanics, but go to 2E for the level of balance and th flavor.