I've been seeing articles about this study floating around on Facebook recently: It turns out parenthood is worse than divorce, unemployment — even the death of a partner.
I LOVE being a parent, but I still agree with this. Becoming a parent wasn't an existential crisis of sad, and it was scary only in places, but it was draining ways that I find somewhat difficult to describe. Like, not just tired-all-the-time draining, though there was a fair amount of that; it's also your-time-is-never-your-own draining, and your-schedule-is-completely-at-the-mercy-of-someone-too-young-to-negotiate-with draining.
And there are all sorts of secondary effects that you either don't expect, or expect intellectually and then are surprised by how hard they hit you when they actually happen. We couldn't really afford daycare, so even with help from nearby family members my wife wound up dropping back to part time so that she could do most of the taking-care-of-the-kids -- and that added some stress, both in terms of "we have less income" and in terms of "How do I get back to full-time employment and is that even possible anymore?" (She did, but it was a gorram miracle -- a ton of effort that only panned out because of a startling stroke of luck -- and she only managed it this time last year.) Firstborn is now nine, and secondborn is five; and I haven't completed a writing project longer than maybe ten pages in over a decade, and I haven't attended martial arts classes (which I used to do regularly) in about six years.
If you need to have your surroundings clear of clutter for your piece of mind, it's going to be a constant struggle (at least, it has been for us). A lot of projects that would have been no big deal before having children become nearly impossible with kids around. (We had a renovation project in our kitchen that, I kid you not, has been in progress for two years now. We've given up; it's going to have to get fixed some other way. Only, "some other way" means "in a way that costs money", and we're only just now starting to have that again.) We're starting to get to the point where we can semi-reliably keep up with laundry and sorting toys and making sure things are put away again, but it's taken us over five years -- basically until the point where Secondborn is old enough to be ready for Kindergarten -- to get there.
So, no: the results of this study don't surprise me at all.