Does Janna need a buff?

She is top tier

Nope. She is rather powerful at the moment because of how well she can protect her carries from divers and assassins.

However, many people don't know how to play her properly.

They are probably just used to Janna players standing behind them during the laning phase (shielding them occasionally) without applying any pressure.

dear god no. she's one of the best supports in the game, if not the best.

Janna does not need buffs

I guess he's expecting an LCS-wannabe MF or Malzahar support. Don't listen to him.