All depends on the players.
I had a poppy who carried me in ranked game (Believe it)
Won top lane (Yep)
You know how? Camped walls. would farm partially, and then I (the jungler) would gank, and then I'd get poppy semi-fed. Mid game, would sit in brush, wait for an enemy, and then boom wall stun OP ignite, hammer to face with sheen and they're dead. Got fed that way.
I had another Poppy
won lane (cuz I was ganking heavily) could NOT hit one single wall with poppy's slam. Nothing. It was garbage. built really poorly and lost us the game.
She has crappy farm, she has crappy early game lane, she has no real sustain and can be out harassed easily. Very team and item reliant. If you let a poppy get fed and farmed.. you must be bad.
True she is OP late game if farmed/fed. Just like every other champion.