Here are my picks thenlet us take mei for example mei has alot of jutsus or elemental jutsus pretty sure in my perspective sakura cannot beat her why?
water jutsu mei has alot feats in the water dragon jutsu and could drown sakura if their fighting in a river or any watery place like ocean too or if they are in plain ground mei could just send signals or receive signals too.
Lava jutsu i know mei could just transform or have a lava on sakura and she goes splat then sakura punches her then mei will obviously cut some of her limbs with that then sakura will grow it from her mitotic regeneration then what? as if sakura has any counters for elemental powers other than healing and punching mei is extremely smart on her powers and could outsmart sakura too. Like there is a possibility mei could just snuck a whole lava on her sakura CANNOT HEAL FOREVER TOO summoning katsuyu won't do much too. It will eventually run out of chakra she cannot even handle the simple acid in the ninja war when they were battling againts kaguya then sakura was about to heal obito then an acid dimension spawned beside her too.
Acid mist like i said she cannot even handle normal acid like that too. Im still wondering why didn't kaguya just spawned sasuke in the acid dimension then send him to the desert dimension of course plot armor same with sakura too. 



Nico robin 
A silent fighter we all know she had her trauma because of what happent to her island also the government was againts her at a very young age.Also she is also can't be considered a heroine who does not need saving because she was also saved once in ennies lobby were the government had her to be excecuted then the strawhats saved her.She had some flaws like having dark humor out of the nowhere then using her devil fruit to her crewmates whenever they were interuppting her reading sessions.She had alot of battles more battles than nami atleast robin knows how to fight her battles like in wano where she foughted black maria alone too. Yeah but real talk what exactly useful did she did eversince dressrosa? beat black maria? had a vegapunk tied to defeat it? then she just rest afterwards? then she is just a "nah id snooze it" character too. 

For karin do i even have to explain it?

Name a character that are strong but never had a another power up or upgrade too.