A good way to think of the H90/H9 algorithms is that they consist of several effect "blocks" that have been curated/restrained/customized to achieve a particular overall sound.
A lot of algorithms are indeed a single effect "block" like you'd find on a FAS or Line 6 device (most of the straightforward delay/verb/mod types) but there's plenty of algorithms that would take several blocks on another device to recreate. Undulator (Plex -> Trem), Pitchfuzz (Distortion -> Pitch -> Delay), Modechoverb (Chorus/Flanger, Delay & reverb in series or parallel) are some examples that come to mind.
Then you've got the Eventide "signature tones" thing like the H910/H949, SP2016, Instant Phaser/Flanger and new things like PrismShift where you play a note or a chord and you get wild results.
I'm working on a video demo with the H90 and FM3 together and there's pretty cool pre/post possibilities. H90 for Polypitch up front and stereo reverb at end of chain, with the verb mixed in parallel, would be straightforward to implement and only add one extra A/D conversion to the core "dry" tone as an example. it is nearly as expensive as a whole new FM3 so I see it as more of a luxury add-on than a core essential in that setup, but variety is the spice of life right?