Since folk have already made perfect posts about Linlin and Lanji, I am going to go for a different choice. :kizabat:
The Supernovas (bar Luffy and Zoro).
This group were supposed to become Luffy’s rivals to the Pirate King throne. They have all had a whole two year head start on Luffy and what have they achieved?
Nothing.
Absolutely,
nothing.
Currently, Pre-TS Luffy legitimately has more achievements under his belt than all the Post-TS Supernovas
combined.
Now, Post-TS Luffy is going to achieve in two months or less what all the Supernovas could not achieve in two
years.
The Supernovas are arguably the most poorly executed idea Oda has ever had.