Different levels of it? What? Lucci made it clear: Stronger Doriki will yield a stronger Tekkai. Doesn't matter if Jabra has a hundred different levels, his strongest Tekkai will be weaker than anyone with a higher Doriki's Tekkai.
Even if the strongest part of his body is his neck(It's actually most likely his legs, since giraffes have powerful legs and his specialty was Rankyaku), it doesn't change that it was Zoro's entire body versus Kaku's neck alone. I'm not assuming anything, we've seen that when Kaku was throwing his entire body at Zoro, he was forcing Zoro backwards.
The levels matter, the gap between Jaburya and Kaku is literally 2 fodder soldiers, Jaburya's strongest tekkai should be above Kaku's regular tekkai.
Kaku never once threw his whole body at Zoro, not did he ever pushed Zoro back while he was buffed up. You're assuming his body could give me enough power to push back a buffed up Zoro.