Don't worry! Universal Controller Fix has been baked into the new Slippi launcher so you don't even need to worry about getting a super good controller, I play on a smash ultimate one I got brand new on release and with UCF I can hit all my shield drops and execute techskill.
do you think the Switch Pro Controller would function with UCF + this online netcode (I have a Pro controller already)? Can you play Melee through your PC via an emulator in the year 2020? I'm sure there's a whole lot of compatability shit the community has come up with but I don't pay super close attention to the scene
trust me man i play with a keyboard literally anything is viable as a controller as long as u can map all the keys to it