The only real drawback of the H90 vs 2 H9 pedals is that the H90 pairs two algorithms / presets together in one program, so there’s not the same freedom to, for example, set up one H9 as a reverb and then easily scroll through various effects on the other one. You can still do it by hand but it does dampen the spontaneity sometimes. And two H9 Max theoretically have 1000 (well 99×99=9801) effect pair combinations while the H90 is limited to 99 per “list” (maybe a good thing to be able to organize everything)
That said, the H90 has more effects, more control options, better on board editing, more robust computer control, and sounds a bit better than the H9, and it will continue to get new effects in the future while the H9 is at the end of development. The H90 also works well without a midi control pedal but one really comes in handy when switching 2 h9’s. (There are workarounds)
Worth noting too that you can get one H9 Max and have the second (or third or fifth) be an H9 core or H9 standard, and both will have all the effects if you have a Max, which could save a little money maybe.

Either way, there are some really inspiring sounds.