Tbf, every SH will be the best in their role. Zoro's role is not swordsman, but fighter/warrior. Thus, can you really blame people for thinking Zoro will be the best fighter EoS. Though one can argue he will be the best fighter if you exclude captains which is a different role.
And tbh the main reason people wank Zoro is not simply because they believe Zoro will necessarily be the strongest, but more so that people struggle to imagine him losing in any context. But that's how the character has been written since OP's inception, can't really blame people for that. Oda wanks him heavily; only Shanks and Oden are wanked more.
Luffy loses literally all the time. Oda is fine making him look terrible, but he usually tries to make Zoro look good, which gives people a false perception of his strength.
The only rival of Luffy's that may be stronger than EoS Zoro is Blackbeard. Kid and Law don't stand a chance at this point. Further to Blackbeard, I can only see Imu, Sabo and Luffy potentially being above Zoro. And that's only if Sabo gets ACoC.