I hate people who make these questions. One Piece is full of Hax using b.s characters.
How does he deal with every Logia outside of Crocodile? How does he deal with observation Haki users? How does he deal with the likes of Bartholomew Kuma who could literally win in a single blow? How do we know if he can resist Boa Hancock? Can he deal with Blackbeard? What will conqueror Haki do to him?
There's a lot more to fights than just strength and durability when it comes to one piece battles. Unless he can literally destroy a moon then he has no soloing potential. I mean look at how observation haki is first displayed by Luffy in the Hawkeye vs Luffy fight, it might as well be like seeing into the future, then post time skip he's dodging the beams from Pacifists that I'm pretty sure are light speed (If I remember correctly the Pacifists got the beams from that admiral with the light light fruit and he kicks at light speed and shoots his beams as such).