Vines in T6 is a big factor of the fight mechanic that could lead to a few kills if not handled properly. Removing these to practice won't make you any better in the real fight.
For your suggestion to work, they should be the same dungeon mechanics, without rewards and without cooldown. Purely for practicing. I could already see people ditching Turn1~5 and normal 6~9 just going for that broken itl95 gear lol.