This is not a valid reason, and we still dont actually know what Shanks wants. For all we know, Blackbeard and Luffy end up fighting for PK and Shanks is used with some ulterior WG shit that he seems to be tied to post Laugh Tale.
We simply do not know where the road is heading, but Blackbeard defeating Law for RPs entirely supports that he does not "need" to defeat Shanks for anything outside of One Piece.
Anyway, I still put my stock on a 3-way battle. Its what makes sense, where Oda can address both Yonko in a timely manner, explore their backstories and history, and do something different from the past battles.
I cannot, for example, see Oda dedicating multiple chapters to Blackbeard and each of his commanders defeating each of Shanks' own, especially not after this chapter. Unless we all expect this shit to be offscreened, theres no way his crew is walking away unscathed