Blackbeard scarred shanks back before Shanks was an emperor, and Blackbeard has a special race enhanced endurance, strength and durability already. Why is it shocking he scarred a weaker version of shanks…
Imu took over the world and has ruled it for 800 years. He’ll have CoC; because he’s not set up as a devil fruit specialist.
You’re coping hard about haki if you think Kaido was right when we as the audience know that Kaido was wrong. Hell, we saw it twice in that same arc. First with Roger vs Whitebeard when we saw Whitebeard was equal to Roger’s CoC haki without his fruit, then again with Luffy vs Kaido when Kaido lost to someone with inferior haki because Luffy awakened his fruit.
Blackbeard will be the strongest pirate Luffy fights, and he’ll do it with his fruits and lineage. His haki not so much.