TrippyHippy
Hero
Classes with their abilities largely based on riding a mount present problems unless the entire party and adventure is set up to feature such things. So many adventuring environments aren't friendly to mounts. That has always been the problem with such options.
If you're writing your own adventures you could tailor it to the abilities and archetypes presented by the PCs of course. The whole are of mounted combat shouldn't just be ignored for these reasons though. How about, for example, having a Fighting Style of Mounted Combat, or allowing a Ranger's Companion Animal to be a horse? Or having a spell to create or enhance a steed? All ideas for consideration.