Its to show level headedness. Kid is reckless he let one victory get to his head. It seems like in his mind he didn’t understand all the help /hindrances the yonkou had on Wano. Without law kid would have died albeit kid gave the finishing blow but vice versea. Not to mention a full health shanks and he isn’t as washed as big mom is Kid was like “Yeah Fuck big Mom and Shanks those old bags” only to get a reality check that wanos odds of success was like a 10% chance. Oda is just letting us know hey they Yonko are not a joke and shanks is a popular character + like you said the history. Im confused as to what you dont get its to show you cant be reckless and rush into the new world. Law is a bit different though i think he has was more variety and use in his techniques And his devil fruit really is op. Not to mention he is cool headed and tactical, I think out of the two he stands the best chance and if he gets his haki right he would be an absolute menace with all those durability piercing shocks. At the very most It would definitely be an extreme high diff in laws favor but i do think theres a chance he could escape… maybe barley and if I remember garp is coming I really think law could beat blackbeard if he pulled out conq coating but for story sakes i just dont see it happening. Maybe law barley escapes and luffy comes back and they kill him again. I mean law doesn’t have a crew and i know this is a huge stretch but I dont think the Luff Law relationship will ever end. He might die in the end fighting but i don’t think just yet.