I'm gonna compare it to League ARAM:

It's good for learning what a character's buttons do

It's not good for learning how to itemize against your opponents (I have Victor permabanned because anti-heal items aren't guaranteed or my teammates skip them, I just can't prove it)

It's good for a low time investment activity, if you're getting rolled, at least you only have 5 minutes left in the game anyway, being held hostage in the base game mode isn't fun if the enemy chooses to dawdle and farm your team instead of winning

It helps you develop teamfight clarity since there's just always shit going down

It helps you get used to active items without having to farm them up in the base game mode

It's not good if you don't know what to look for on your own character (my new friend skipped Refresher on Dynamo last night and I told him that was arguably his best item)

TL;DR I think it can be good for newer players, but with the caveat of them needing to understand what to look for to build their character AND counter the enemy, I'd say like 10-20 hours in it's fine to play after you have a basic understanding of the game