From a game play perspective i don't see anything wrong with westernization, especially from the perspective of a country starting in the western tech group.
It's a fair point that maybe the actual leap from tech group to tech group happens too fast, but since military units don't even change anymore this doesn't produce any tangible difference. Depending on how far they were behind it takes significantly longer than the "westernization" process to actually get caught up in tech and, just as importantly, ideas not to mention province development.
If as a player of a European country you're having trouble combating recently westernized foes then you're probably doing something wrong. Usually the morale and other combat modifier bonuses you get from ideas which, unlike those in lesser tech groups, you have had the luxury of investing in are enough to turn battles in your favour even if somehow they have caught up in tech or outnumber you.
From the perspective of non-western tech groups i've never found the westernization process itself too hard to deal with, but its also not too easy and by the end your country is usually de-stabilized, lacking in legitimacy and monarch points, initially behind in tech even with those of your former tech group, and in some other sort of trouble. Like i mentioned above it also takes a good deal longer to actually catch up in the western tech group to the point where you can meaningfully compete with major European powers. And that is if you can get to this point at all considering that already powerful European powers are also lucky and tend to have some pretty good national ideas combined with the ideas they get to pick. Morale in particular i have always found hard to match and its probably the most important combat modifier.
Moreover regardless of how easy the mechanic is it is still quite possible and not even all that difficult to militarily conquer any country in Asia, Africa, or the New World, a good deal easier than, in my opinion, it ought to be. If the complaint is that the AI westernizing makes this a bit more difficult my response is that it should be.
The point about India and China both westernizing and then allying making it so that overseas expansion is impossible unless you can beat their giant armies is a good one that should be addressed but it doesn't have to do with westernization, but rather the AI diplomacy. In nearly every one of my games France, Spain, and Portugal or England, Spain, and Portugal all ally and all join each others offensive wars half way across the globe with African and Asian minors. This is just as annoying, especially when trying to play in Africa or Asia.
