Question

Is EV training really important for in-game playthroughs?

Answer 1

For most in game playthroughs it’s usually easier to get new Pokémon with type advantage than to EV trained your older Pokémon, so there isn’t much point in that.

Also most in game battles don’t have fully EV trained Pokémon, and as long as your Pokémon are similarly leveled as your opponents, you should be completely fine without EV training.

Comments

Leveling up your older Pokemon is easier than getting a new Pokemon.

Answer 2

It doesn't matter much as long as you have a super effective Pokemon against the gym leaders since they specialize in only that one type (kind of like a monotype team), unlike VGC battles, you can use your potions during battles, and if you are looking to speedrun the game, it is annoying to EV train, the fact that you can also teach your Pokemon good moves because that is not as time consuming as training EVs, you can do that for competitive battling because that is important.
I've hoped I've helped!

Answer 3

One important difference between in-game and competitive is that you can use Pokemon that have higher levels than in-game opponents. So if you lose a battle in-game, then the fastest way to win is usually taking your highest level Pokemon and raising it by a few more levels. Compared to level grinding, EV training is a waste of time.
source: every Bulbapedia page that says someone uses a Pokemon lower than level 100

Answer 4

Of course EV training is important for making up for the weaknesses or strengthening it even further. It is mostly important during the later part of the game. U can use EV items to shorten the training too.

Comments

EV training can make the game easier, but it is in no way important. Your Pokemon could have zero IVs, EVs, and a hindering Nature, and you could still be able to beat the game. They're completely unnecessary in-game, and only matter in the competitive scene.

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Ok but why downvoting?

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The answer suggests that EV training is important for in-game playthroughs, which is not true. The random EVs you get from playing the game normally are more than enough for beating AI.