well one can certainly beat the game with no ev training or targeting high IVs, but they do help quite.
after a point, EV training is really so simple that in my opinion is very worth it, because of power bracer, power lens, and power anklet.
so you just go to peridot ward under a bridge, where there are 2 woobat patches. and you battle them over and over holding either power bracer (for attack) or lens (for special attack). when they reach 252, u switch to anklet to finish with speed, and then you are done. for every pokemon that has at least 2 attacks with 20 PP or more, the process should take very very little time (2-3 pokecenter heals per pokemon. i even teach them moves like cut for this and then replace them afterwards) (i use cheat engine to speed up the game x5 too since there is no fastforward button like at emulators).