To put it simply, youll be useful no matter what more to the team cause of the Moonstone plus moonstone heals herself on RW hence why its the best mythic to go tank with on her in my mind.
In the end...
karma top is alright... but in this day and age you get outscaled way to quickly so you can only flex her into certain matchups if im completely honest.
Counters
Camille
Champion
Outscales ya pretty hard if the game goes on for a long time.. and u cant follow up upon her split pushing
Nasus
Champion
A Threat due to him being able to outscale you and usually more seen as a threat in lower elo so his bannable.
Tryndamere
Champion
counters you pretty hard, you cant really do anything to him when he zooms away from ur W either.
Fiora
Champion
Also outscales ya pretty hard and she just demolishes you, so worth the ban in the long wrong cause fiora just shreds tanks overall.
A good fiora will also know how to cancel ur W even if ur just trying to hit it with her, but be sure to baite her with it and keep yourself out of range.
Riven
Champion
pure annoyance too mobile for karma but isnt as a big threat as fiora who can cancel pretty much karmas entire kit.
Akali
Champion
Akali... youll be able to handle her if you play safely enough 1v1's arent as hard but youll need an item at least to keep up with her so u can outsustain her.
Irelia
Champion
She's too quick with her blades, id rather not deal with her she's one of thee few champions who counters karma pretty damn hard.
Jax
Champion
Outscales and just pushes like crazy would be an instaban almost for me.
Garen
Champion
just annoying in general you wont do dmg to garen whatsoever....
Wukong
Champion
His early dmg is quite absurd when he gets sheen so stay out of site and wait for items.
Yorick
Champion
outscales and too much pressure just from his kit alone, but u can poke him down in the early.
Gangplank
Champion
Instaban, id rather just not deal with him when he can be at an distance and just not intereact with you.