User blog comment:Alonlah/Poppys viability in the current meta and her status in the PBE./@comment-8506165-20130817072158/@comment-8506165-20130821024135

Her mana costs are high relative to her mana pool, yes. As you mentioned, Diana has vaguely comparable mana costs until you factor in her ultimate, and she has higher base mana and mana regen to compensate as well as it being easier to itemise mana fixes on her. But Diana's mana costs /are/ actually fairly high; compare her to, or even  (to pick three different character archetypes) and you can see she's hardly the most mana-efficient champ.

And if you don't think her farming is abysmal (forgive me if I misunderstood, but that seems to be what you're saying) then I can only assume you're comparing her to someone like - although even LB can clear a minion wave with Distortion/MimicDistortion in desperate need. The terribad farming, combined with lack of innate sustain, combined with lack of good disengage from trades, combined with mana issues, makes her a very poor toplaner who will usually end up relentlessly zoned without serious help from the jungler unless her lane opponent is... well, awful. She lacks almost everything a toplaner wants. Just giving her mana won't fix this, or you could start Sapphire Crystal for a Sheen and win your lane.