That is headcanon bro. We have no idea how the two paramecia would interact. As for haki Cracker has stronger haki than Doffy so in head yo head clash of paramecia powers Cracker should have the edge. In terms of CQC, IIRC Luffy was not able to land a single blow on Cracker in 11 hours whereas in Doffy fight he landed quite a lot of shots in that 30-60 min period. Not to mention that Luffy against Cracker is stronger due to haki bloom and battle experience.
I am not referring to Doffy turning biscuit soldiers into strings here.
When it comes to fighting Cracker, 2 things make him look bad - effective combat style, which Luffy didn't have and beating him at his own game, which Luffy also didn't have.
In case of Doffy, both of those things are present - effective cutting style of combat as well as beating Cracker at his own game through Awakening which completely overwhelms the biscuit soldiers because size is king here and Doffy turns good portion of a town into strings.
I am not sure whose haki is stronger, I don't think Cracker used haki on his biscuit solders, except the one he was inside, perhaps.
They were simply hard, just like Perospero's candy was hard and Luffy didn't break it at first while Amande easily cut through it.
Doffy's post-GK performance is tainted, he was handling Luffy well before it.
Also, I didn't see any haki bloom between Doffy fight and Cracker fight.