This question reminds me of a conversation I once had with someone who called me "immoral" for using DACUS in Smash Brawls, which he considered cheating since the developers didn't intend for it to be used.
Now I stopped playing Pokemon games after the 4th generation but I always thought they should just go ahead and make EV training an official game mechanic and put a tutorial in it. I mean it's there and it's the best way to give your Pokemon good stats, so players should be able to know about it if they want to. I don't think it would hurt to do the same for DACUS.
So to answer OP's question I think time-traveling and EV training are similar in some ways, but I also think intending for us to be ignorant of EV training is much more silly than intending for us to play Animal Crossing day-to-day