Viego perfectly encapsulates the current gameplay philosophy of Riot: he is manaless, has sustain (or has access to it through runes/items), his kit fixes his supposed problems (he should be a melee champ, yet he has 650 range spammable Q, getting harassed in lane due to his melee nature is fixed by his inbuult sustain).

Add all these stuff up and you get a mana-less, sustained early game bully, who can endlessly shove wave after wave, forcing the mage to spend their mana, or just force trades to burn their mana even faster because he can just heal it back. And even if the mage survives all this until Chapter/Tear, Viego can just 100 to 0 them after 6, especially now that Seekers is garbage. Aaaaaand then Viego can choose to either be a splitpush menace or snowball a teamfights through his invulnerability and grasshopper execute ult. He just does too many things, while he can just straight up stat check or choke out mages from mid, while also scaling really really well.

Edit: Terrorising mid lane, even tho he was designed as a jungler... really good job :)