The Gorosei acknowledged Marco as a pseudo yonko. Either he would stop Teach or it would have to be the marines or another yonko doing it. In the end Marco is a capable YC1 who can hold of a yonko or an admiral but Teach was beyond his pay grade. Same scenario for King or Katakuri. Also same for Zoro and Sabo, most likely also true for Ben Beckman. They currently lack the strength, the leadership or both to be yonko.
Marco - lacks the strength, respected by all WB-affiliates
King - lacks the leadership, Sasaki, Who's Who and Queen questioning him
Katakuri - lacks the strength, respected by all BM-pirates (except Flampe, Perospero)
Zoro - lacks the leadership, Nami, Chopper, Sanji questioning him
Sabo - lacks the strength, respected by all revolutionaries
Beckman - ???