Kaku is in his literal strongest form, using his strongest attacks as a call-back to EL. The exact same form that Lucci has, that matched and sent a CoA-infused G5 Luffy flying with a nameless, basic haki-coated punch.
Kaku uses an upper-end named attack against a Base Santoryu Zoro using simple CoA. He pushes Zoro back for a panel and gets immediately knocked down.
Lucci and Kaku are using the same form. Lucci remains superior but there's not much separating them portrayal-wise anymore. And Kaku performed worse using higher-end attacks than Lucci did which potentially balances out any difference in strength.
Zoro objectively performed better than Luffy here. Note: Both Luffy and Zoro would utterly shitstomp Lucci and Kaku if they were serious so it's really not that deep. But Zoro held back his high-release CoA as his swords were not smoking, CoC-coating as no lightning, KOH and Asura. Luffy held back CoC, fought in his strongest form and looked worse off than Lucci did after the battle. Again, does it really matter? No, but it's worth noting that Base Zoro with hardening is comparable to G5 Luffy with hardening.