Originally Posted by
Zoma
Keep in mind it's not just the strength of Kaidou (although I imagine that is probably frikkin huge), it's also the strength of his crew. Kaidou was already strong enough to become a Yonkou before getting SMILE, and now he's added several hundred Zoan-types to his crew.
DD's fruit does seem pretty strong, but it probably has some weaknesses. Maybe they'll just wait for a cloudless day, then shove him into the ocean. Maybe there is a limited number of threads he can make at one time.
Assuming equal Haki and physical skill, some fruits are better than others. Akainu's Lava > Ace's Fire, Luffy's Rubber > Enel's Thunder, etc. It's a bit of rock, paper, scissors for some of them.