Are there any drawbacks to using candies to level up your pokemon?
I'm very much an old school Pokemon fan, only played the first 3 generations of games so I haven't kept up with the meta. From my understanding, rare candies were quick and easy ways to level up a pokemon but had a major drawback, EVs do not increase and cannot be recovered if you're max level.
In my playthough, I have amassed hundreds of experience candies and rare candies and am contemplating using them or selling them. EVs could be increased with the grit rocks and leveling up pokemon to the 60s and 70s seem easy to me so I don't really know if I even need to use the candies except for my highest level pokemon.
Are there any drawbacks to using these candies to gain experience and level up my pokemon?
I don't want to skip out on increasing stats if I don't have to.
As far as I know, there are no evidence of drawbacks to using candies to gain experience. Bulbapedia only states:
When consumed, it will grant a single Pokémon a moderate amount of Exp. Points.
So they only give you experience, like when defeating a wild Pokemon. Nothing bad or irreversible can happen.
Also because EVs are no more present in Pokemon Legends: Arceus. IVs and EVs were replaced with ELs (Effort Levels) which can be increased using https://www.serebii.net/legendsarceus/effortlevels.shtml as you pointed out. No more battle are required to max a Pokemon, so you can apply those items even to a level 100 Pokemon.
I prefer to save them to fulfil Research requests, maybe for those Pokemon who need high levels to evolve. Leveling with candies is a quick (and lazy) way of doing it.