The primary downside is how it could affect public play, particularly given the prevalence of cavalry, and make it quite unenjoyable to deal with getting knocked over by teammates or even trolled by them. This could be lessened by doing something like making the duration of team-bumps and team-knockdowns shorter than the duration of those on enemies, but there’s still a lot of potential for abuse in public games.
I also don’t think a flat HP or armour nerf is the right way to go. There are much smarter ways to redefine the balance between the classes that promotes more skill-based gameplay, a few examples of which are in my first post on this thread.