Ichigo vs Ikkaku, Ichigo vs Renji
Hm.. just a guess.. Ikkaku is stronger than Renji right?
Renji even was under Ikkaku, iKkaku trained him and even now Ikkaku is respected by Renji. Well, what i wanna tell here is that Kubo messed up and very much. Remember the fight Ichigo vs Ikkaku, right after he got to the sould society? He defeated Ikkaku without any problems..
Assuming Ichigo has Enhanced growth rate, after few hours or days he BARELY defeats Renji- who is NOT stronger and should be even weaker than Ikaku. Hella he didnt even defeat Renji, renji almost killed him but then the strange eye-look came from his eyes and yeah he won...
So hm whats my point?
Kubo doesnt think his story very accurately.. First he draws fights and only then he generates his story, which may not be up to what he said earlier. It was even said in the manga that Ikkaku is a captain level fighter and the only reason he is 3rd seat is cuz he wasnts to serve under Kenpachi.