Because he needed something MORE than an half-assed PU to beat Doffy.
He needed Law.
"He needed more than" cope
Doffy is the only person to lose to boundman in the whole series (lost badly too).. the only one beside Cracker to lose to G4 (no fs, adcoc, adcoa)
He needed hours, plot, escape, food, rest, FS just to match base Katakuri
He needed law to beat Doffy + Bellamy and trebol.
Comeback when Doffy has adhaki and hype as one of the mightiest or is seen superior by Luffy's own words.
Luffy never saw doffy superior to himself. He knew g4 was enough to beat doffy and he did that convincedly.
That's why Cracker is where Oda capped Doffy at.
In your logic, Cracker > Katakuri since Luffy needed nami and homies help to survive and win.
Cracker actually fought 1v2 almost the whole fight while Doffy never fought 1v2 even half the fight.