It took him 10 days to barely beat Aokiji even though He has a natural advantage over Aokiji (magma>>>Ice). If he's having difficulty with someone that had a disadvantage to him then I don't see him beating a Yonkounot exactly some say that akainu is on yonkou level
OT: If the strawhats+Law's crew have only a 30% chance of taking down Kaidou. what makes you think Luffy alone can solo Big man Lol