Yet this arc is a little different from the others, his welcome fight in WCI was Cracker and he indeed demonstrated he could now deal with Doffy level fighters without much difficulties aka he was ready to try something stronger aka Katakuri. But his welcome fight in Wano has been Kaido, he got demolished and recognized he needed to train and indeed we were feed with Luffy training, one way or another, since Udon aka the next chapter after Kaido one shot him.
Also now Luffy clearly stated that he is going for Kaido to the top of the dome befire being stopped by BM. King is completely out of his way, Luffy is not looking for King and viceversa and also their targets are different: one is looking for Kaido the other to secure Momo/get rid of Sanji. And, this was stated when Zoro carried away Luffy after Apoo first attacked them, they can not take too much damage before their fight and if Luffy fights King then there is no way he after that has even the strength to put up a good fight vs Kaido even as part of a team (if we exclude gargantuan levels of plot armor). And finally Luffy is already eating tons of space, if now he also steals King, or even just Jack or Queen from characters like Sanji, who had his last proper 1 vs 1 in Thriller bark (13 years ago) or even Zoro who has Pica 2 arcs ago or Jinbe who needs space too as the new SH that is too much from Oda.