Yes by definition they are. Even if they have not lost directly against either Roger or Whitebeard (all lost against Roger, including WB, but to be fair, Kaidou was younger), it could not be more obvious that Roger and WB are supposed to be the wall they could not overcome, by BM´s own admission who admitted she might have done it with the help of the giants though.
Great Pirate Era was WB´s era.