Personally I’ve noticed you could probably stick to the level one trainings to get through it alot faster. The 2nd tier for speed for example becomes abit harder to hit (unless your just THAT good). The first tier grants 4 EVs for whichever stat you picked however your attacks WILL get stronger as you progress to the point where you can OHKO most of these balloons and in doing so, you are granted the Large Training Bags which grant 12 EVs. After maxing out an offensive stat then you can start the other levels without too much trouble. For me personally this seems like a much easier and much faster way of maxing out your stats.