Plumbing is way, way easier than drywall (in fact I would go so far as to call the supply side of it “easy,” including soldering copper pipes); it’s just that the penalty for failure is so much higher.
I partly agree and partly don’t.
Plumbing as a field is way broader than installing drywall, and there’s a ton to learn. No single plumbing task is really harder than hanging drywall (except maybe welding), but doing all the drywall in an entire building is a hell of a lot easier than doing all the plumbing for it.
I’m only talking about DIY plumbing a single-family house, and I only said the supply side was easier. The drain side is more complicated to understand, with the slopes and venting and whatnot.
That’s how I started out, too. Not only does it take forever to dry, it’ll crack and slump. And then, of course, there’s the interminable sanding.
You can also play with the later coats, going with a thinner consistency so it fills the little holes better and you’re scraping most of it off. Watch a few youtube channels of pros, it’s time well spent to save time later.