if zoro was the better fighter why has he always being incompetent to leave the strongest opponent to the weaker crewmate (luffy)
Who? Morgan? Zoro Dealt with him
Buggy? His DF Counters Zoro so Luffy had to Fight Him
Kuro? Zoro had to carry Usopp & save Kaya so Luffy stayed with Kuro
Krieg? Mihawk Came
Arlong? Mihawk Injury
Baroque Works? Zoro Dealt with them all
Mr. 3? Zoro was Trapped
Wapol? Zoro wasn't even there
Crocodile? Logia & only Luffy could Fight Him
Bellamy? Luffy told Zoro to let him hit them
Enel? Only Luffy can Fight him
Foxy? Game Rules
Lucci? Both Luffy & Zoro faced him in Water 7 but in Enies Lobby Luffy wanted to take Revenge himself
T-Bone & CP Train? Luffy told Zoro to handle them
Moriah & Oars? It was Team Work
Kuma? Zoro faced him
Pacifista? Team Work again
Hody? Zoro Defeated him First
Hyouzou? Luffy faced him & said he was "Strong" then Zoro One-Shot him
PH Dragon? Zoro Dealt with it
Caesar? Monet saved him from Luffy & then Zoro Dealt with her (And he wasn't Strongest anyway, it was Vergo)
Fujitora? Zoro handled him so Luffy can pass through to fight the Weaker Doflamingo
Katakuri? Zoro wasn't there at all
Urashima? Zoro scared him & not Luffy
Hawkins? Zoro handled him
Apoo? Zoro handled him
Kaido? Zoro protected Luffy a Dozen time & was forced to retreat because of Both Kaido/BM
So you should learn by now that Zoro is indeed Strongest but Oda always make Scenarios so that it's Luffy who crushes the Villain's Dream, after all he is the Main Character