I did a new emulator config with another way for remapping commands (native emulator mapping is Right Ctrl for fire button and something else non-standard, that's why I did the remap which may cause lag). Try downloading again, it might be improved in that area with the changed config file. It's on CastlevaniaAGA_Win64\FS-UAE\Configurations\Default.fs-uae so you can edit and alter mapping if you use a controller and want other button maps etc.
About Genesis, I was told (by contact working for the IP holders) that, as long as it's on a niche system like Amiga, I'll be fine. If it goes to modern PC or even the popular Genesis, there could be legal scrutiny. New Genesis games are made into cartridges by the Chinese to be sold by the thousands at AliExpress, so, money involved = big problem. But, I could do a Genesis game with original IP using this codebase or parts. ;)