I bought Ulysses license few teras ago (when it was still non-subscription). I use it intensively dering my college. The closest one with Ulysses is (IMO) iA Writer. It’s one time purchase.Been using Ulysses for quite a few years now. It is great, but I don't believe it even remotely deserves to be a rental app. It had basically all of its features years ago, and these days they just noodle around with little word counters and screw up the interface periodically to keep the Mac and iPad versions parallel.
Sadly, I'm rather locked in with many hundreds of thousands of words written in it -- but I'm always on the lookout for an alternative. I've checked out Scrivener a few times, but the interface looks a bit kludgy and sync seems like a full on disaster as the OP said. If they ever get around to overhauling it, I'd give it a look. I don't mind paying for quality tools, but Ulysses pulling $40 out of my pocket every 12 months to add a "writing stat tracker" or whatever doesn't sit well with me.
I do love writing in Pages, but I'm filled with dread at the prospect of setting up a zillion folders and tags to organize my stuff half as well as Ulysses does.
However, I found that Scrivener is much better fit for my needs. I don’t have concerns on Dropbox sync (I used the free one, but capacity is around 18gb).