Beating Ace or Law is far different from him beating the character with the canonically highest display of Haki in this series (barring Joyboy), but go ahead and believe what you want lol.
I guarantee you that we do not know enough about Shanks to make hard claims that he and Luffy wont fight, especially when Luffy himself only agreed to ally with Law as long as it wasnt about fighting Shanks first.
I have my PFP for a reason, its to reiterate the fact that Shanks reacts to Luffy in an antagonistic way, not as an ally (unless you think that face means he just wants to congratulate him lol). The dude decided to attack his fleet members, why are we still denying this?