Why don't people complain about Diana more?

She does have brutal gap closers, but she can't use them to get OUT of situations. Riven is annoying because she can run away as fast as she can run at you; Diana is all engage, all the time.

Mostly because it's far less easy for her to faceroll in lane.

Snowballing Dianas are brutal, though. I agree.

no mana cost? no retarded mobility? no no cast time? no good in all stage of the game? no

Juggernaut update and armor/magic resitance items rework give her hard time bc she is meant to kill squishy targets.

Because while Diana is faceroll easy with absurd damage she can't 1v5 instantly, she can't stun an entire team and she can't dash in change her mind and run off. She requires landing a short range and slow awkward skill shot to get a dash ever 6 seconds and using it essentially gives up any chance of escape. Fed Diana can kill one person with little to no counterplay but riven can kill your whole team.

No lifesteal. Has mana. Can only dash to a target once, requiring a conditional skillshot/spell to land to get a single reset. Easier to gank against and kite if you know how. Not as faceroll to win. All-in is just that, can't bunny hop out and come loaded with spammable hard CC. Can't AOE range execute. Can't split as well as Riven. Weak as hell pre-6, giving a fairly lengthy safety window.

Erm... I don't see how Diana is anything like Riven, other than both being melee fighter/assassins.

Diana has weaknesses.