I know this is 100% broken for EV trainers and whatnot, but i was thinking about for the Sonata Race Tracks, if you get 1st in 1-5 races in a row you get like 1-2 EVs in speed for the pokemon that got 1st respectively.
I know it is broken and sounds broken. But it’s just an idea for those Pokemon who needed to be grinded and wasted all the HP Evs on the level trainer audino (seriously, that is an issue wasting all your evs on HP instead of like attack or something)
About your second issue: You can undo EV training, if you buy the respective Berries in the Market in Helios City.
yes i am also aware of the ev resetter. but i still want some evs anyway though. 
I think I don’t quite understand your issue. Why would you want 1-2 EVs in Speed for winning races? You can just train with the EV Trainer for Speed and get 3 in 30 seconds.
Do you mean Evs on top of the 510, or do you mistake EVs with IVs?
First of all, i’m on a randomizer. So for some reason the EV trainer’s pokemon are randomized, because when i wanted to train attack, it trained other pokemon. 
2nd, i didn’t mistake evs with ivs.
people on randomizer dont need evs lol since you cant even play online but its up to you
EVs aren’t just for competitive play.
give me an example please ?(im serious ive never played a challange run
then play one! also challenge*
Im not trying to be offesive because ev only adds little stats so its not that useful but i do agree thatyou should ev train since in pokemon insurgence the elite four will have a competitive team(an ingame npc said it)