No, It’s actually the other way around. The Eventide H90 can run two algorithms at the same time, while the H9 only runs one at a time. The H9 platform is also basically finished at this point — Eventide isn’t releasing any new algorithms for it. Even the H9 Max already has everything that was ever made for the H9, so what you see is what you get.
That said, the H9 is still a great grab on the used market. The delays, reverbs, modulation, pitch, harmonizer, and distortion algorithms are all top-tier, and a lot of them came straight from Eventide’s big rack units and Factor pedals. Sound-wise, there’s no downgrade at all. If the H9 and H90 are running the same algorithm, they sound the same.
Where the H90 pulls ahead is in flexibility and live use. You can run two algorithms at once, the routing is way more advanced, and the footswitching is set up better for performance with easier bank changes and preset control. It’s just a more powerful, more gig-friendly unit overall, not a better-sounding one.