so... after 2 years ? why mana potion got removed?

Nope , who has mana problems ? Unless your a filthy Lethality Pantheon in top lane .............

Because mana potion gave too much sustain and riot goal was to kill the laning phase as fast as possible so we can have 10 min team fights instead of 25 min

I assume it's the same reason they removed stealth wards from the shop.

All they do is give an even bigger advantage to the side that gets a lead and has more gold to spare.

Fuck no

When they removed them they litterally rebalanced the base mana and mana regen stats for every champ. Mana pots were just holding the champs back since riot was forced to balance all mana champs "in case" people were buying a lot of mana pots. We still have if people need mana.