I, personally, am in the "MP is the best thing since sliced bread" group. Even if I blob up massively (as in, ~200 provinces-massive), and my ruler stats are only average, I always have enough points for techs, ideas, and then some to build up the essential buildings in pretty much all provinces:
-temples
-constables
-armories (often training camps too; max tier in designated recruitment provinces),
-maxed out naval buildings in all coastal provinces
-manufacturies. Everywhere.
Trade power? Check. Money? Check. Manpower? Check. Forcelimits? Check.
Sure, you have to take into account peace deals and coring as well, but if you play smart and pay attention to what vassals you can release, and whether your potential vassals have claims they might be willing to buy from you later on, you can avoid coring AT THE VERY LEAST half the provinces you conquer.
Every single campaign I've played so far - an'd I've put more than 400 hours into the game, if you were wondering - I've never come to a situation where everything would ground to a halt just because I got a shitty monarch or two: I just expanded in different directions, where I could avoid paying for my conquests myself.
I will admit, though, that at the start of the campaign, catching up in techs takes a while, it's hard to afford good advisors, and if you get a poor monarch to boot, the take-off might be slow. However, a few decades in, things speed up and about a century later, it is often money that becomes the limiting factor, rather than monarch points.
I don't think people should dismiss the MP system after playing for just a few minutes and getting a poor first impression. The negative responses towards the system, I've come to notice, tend to come out as either purely, or, at least, half-theorycrafts, mixed with experiences of a slow start.
I say just let game roll for a few decades, it'll grow on ya