Indeed, that's tricky.
What Jeffrey said certainly works, but....I think this is a great example of how fingerings can be influenced by musical decisions -- and I think 5-4 could be quite fine. Ideally, fingering decisions aren't only about how the notes lay out; they're also about how you think of the passage and how you're going to be playing it.
You say the fingering feels "weak." I think I would want
to play it "weak" (just talking about that first set that you talked about), in order to have lots of room to build from it. In order to make that work, you'd need to play the accompanying LH notes very
soft (related to what Jeffrey also said). I've worked on the piece some, and that's how I've generally done it (and using 5-4). If I thought I might want to play that set more strongly, I'd definitely use 5-3 -- but I don't think I'd ever think of it that way.
This is also a great example of how deceptively complex and difficult this piece is. We could probably have a similar discussion about almost every note of the piece, and in most cases, probably an argument.
Edit: Forget what I said.
I played around with it a little more, and I think I might use the 5-3 fingering suggested by Jeffrey no matter how I want to play the passage. But 5-4 can work well also, provided you're conceiving of that beat as "weak."