Now theres a feature that I adore in FE3 & FE5, called dismount, which forced mounted units to dismount indoors, it wasn't perfect and probably needed some tweaks, but which game do you think handled it better overall?
I think personally I'm going to have to go with FE3, while FE5's does it fairly well, you still get people who are amazing off horseback like Dean and other people, I feel in FE3 it actively makes you use your foot units more, although if you have say Palla or Sirius in Book 2 it doesn't matter too much to them, but it still encourages the use of your foot units more than FE5, in my humble opinion, but also didn't hamper the mounts quite as much.
Also for those of you unaware with how dismount works, in FE3 mounted units could generally only use Lances (As a cav or paladin) on horseback or Bows (as a Horseman) but on foot they had to use swords, unless they were a horseman they kept their bow on foot so they were basically a hunter indoors, however they didn't have to worry about a separate rank because FE3 has weapon level as a stat.
FE5 Swords were a seperate rank, so characters are actively hampered, however as mentioned before certain super good mounts like Dean also have really good sword ranks, and certain characters like Brighton had a good skill to compensate even without a mount.
Also your stats would be lowered when you dismounted, to just put that on-top of everything. Someone could probably explain this better than me, but thats my tiny summary.
(Also yes i'm aware Tearring Saga and Berwick expanded on it alot, I just wanted to see opinions in a FE context first)