D&D 5E - Can you Dodge and Attack on the same turn?
I agree, and I'd almost be tempted to argue that attacks against you had advantage if your mount was throwing you around in the saddle by bouncing all over the place.
Feats are expensive. Don't nickle and dime them away to nothing. And definitely don't turn them into a disadvantage because you prefer heavy simulation in your fantasy magic and elves.
Seriously, 3.5 is a great system with abundant feats and heavy simulation. If that's the type of game you want to run, it's probably a great match for your DMing style.
5e is a more lightweight game with less rules emphasis on realism in order to make a quicker and more cinematic game. Feats are rarer and are according to the designers are supposed to be a big bonus to someone doing something the feat focuses on.
If you have mounted combat, I'd rule if you make the mount Dash, you move with it. If you make the mount Disengage you disengage with it. If you make your mount dodge, you dodge with it.
You're spending a feat on something that inherently will only work part of the time. In that tavern brawl? Useless feat. Splunking in caves, or exploring a ruined temple? Also likely useless. So the times it can work, it should work well.
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