i think people give too much weight to what yamato says like its canon. she guessed that kaido was weakening because the flame clouds were dissipating, but is there any evidence to that, really? kaido took it as far as he needed to go, didn't get interrupted, and kept fighting at a high level the whole time. i think if anything its "kaido is focusing more on the fight and less on flame clouds" more than "kaido is getting weak".