Disclosure: I have yet to explore the works you've mentioned above, so please pardon my ignorance and lack of relevant examples [currently going through Innocence is Lost].
I mean, I'm brand new here so what the fuck do I know, but if I may wax poetic on the topic of sci fi VS fantasty for just a second:
I always considered those two genres as two sides of the same coin. I'm sure that hot take is about as groundbreaking as florals for spring, but humor me, if you will.
If the steampunk setting is powered by magic instead of technology, could it, arguably, fit more within the fantasy genre? Conversely, if the steampunk setting is fueled by technological advances with magical elements being a more cultural aspect VS a technological aspect, I feel that could snugly fit within the sci fi category.