I think we need to accept that Kubo wanted to make Ikaku look powerful but unwitiingly made him look hella weak sodon't be suprised if he's fighting stronger foes later. Zaraki was hyped and then looked weak with Ichigo but later on the hype proved true. Ikkaku's hyped as being greater than Renji so just watch him prove it true later.
1. The two that Renji and Hitsugaya were fighting could've been a lot stronger than the one Ikkaku was fighting.
2. Ikkaku's much stronger than most think.
I'm pretty damn sure that if Renji and Hitsugaya were fighting at max power at the beginning, they most likely would've been able to force their opponents into their release modes while only using Shikai.
Go back and read the chapter again. Renji states he wasn't sure if he would of won without the limiter. The limiter's surprise influx of power allowed him to overwhelm the arrancar who wasn't going all out.