In this regard, does leveling Pokemon with Rare Candy make them weaker?
Basically they are extra hidden points that you getbybattling. When using Rare Candies, you don't gain anyofthose points, so your Pokemon could beweaker.However, if you have trained a Pokemon from alowlevel up to level 50-60 you will probablyalreadyhave all possible EVs, so using Rare Candiesdoesn'tmatter.
Also know, is exp share bad for EV?
If you're going to use the larvitar competitively,thennot ev training it is not a good idea. The expsharestill passes on the evs so you can still use the expshareand be fine. If you don't want any evs on it then put itin thedaycare.
From Generation VI onwards, the Exp.Sharereturned to being a key item that shares 50% oftheExp earned in battle with any Pokémon that areinyour current party and did not join the battle.