Unless you're map painting and aim for as many provinces as possible, isn't it stronger to have 100 dev in 2 provinces rather than spread over 10+? More effect from buildings, easier to defend and faster institution spread, while still costing the same amount of warscore and AE all sound like a pretty decent deal to me.
I can see the nuisance when trying to fulfil missions though, but try to see it as getting a bigger reward (in terms of strength and land quality) for succeeding with it while using every trick to keep AE relatively managable.
I guess you could always try for emperorship and get like 4000 dev for free by passing the reforms.
You're absolutely right, in theory, having 2 provinces rather than ten with the same development is far more efficient, for the numerous reasons you talked about. But, and there is some of them, the AI development thing does not affect only the two provinces we're talking about, but the entire world. So those nice two provinces you took, are nice and well developped, but so is all the other one around them, and in the grand scheme of things, you just took two provinces, but two expensive AE provinces. And for a 1700 game, this is absolutely nothing. Going for ten provinces instead of two is a way to weaken your opponent, if your goal is to end the Ottomans threat and you're going five provinces per war, you won't go far.
You can see it as you depict it, like a more i need to use all the tools kind of thing, wich makes you feel more accomplished. But for me, it feels wrong, it sucked the fun out of my games. This change affect all players because it's effective on all difficulties. And i do remember a time where i didn't know how to truce juggle, how to optimize my AE reduction, how to break coalitions. I think a lot of people are struggling because of this, and that's why i'm talking about it.
The game always allowed to play tall, and nothing has changed on this side, but it has hardened by a lot the playing wide way. I'm certain that if tomorrow i go for a Portugal only colonial game, fighting in the new world or some minors in Indonesia, it won't bother me that much. But it makes it tedious if your fun is to conquer Europe has a minor in Africa, or any expansionist playstyle you like.