Scott

Shanks should wipe the floor with Blackbeard regardless of what Devil Fruits he has since haki counters devil fruits and is the only way to hurt the users... Especially logia users. Shanks is the strongest Advanced Conquerors Haki user and all his other haki is top notch. Blackbeard would have had a little bit of trouble with Kidd while Shanks one spotted him without really even trying. Roger who was also devil fruitless was the strongest in One Piece due to his high level of Advanced Conqueors haki. Blackbeard doesn't have Conquerors haki, so unless he is hiding the fact that he really does have it, then he really doesn't have much of a chance regardless of what he does with his devil fruits. Shanks could probably attack before Blackbeard could even make a move with any of his devil fruits to be completely honest... Especially with Shanks Advanced Observation haki being a thing. It should be a very one-sided fight without including plot armor or some kind of random huge leverage on Shanks that Blackbeard comes up with.

Well seeing how no one could hurt Kaido at all without Conquerors haki and even with Advanced Conquerors haki... It was still quite difficult to injure Kaido badly makes me think that Advanced Conqueors haki would be much stronger than Blackbeards devil fruits. Armament Haki literally is the only way to even make contact with Logia users in order to hurt them and can even neglect a lot of devil fruits abilities when initially making contact. Using Advanced Conquerors haki should absolutely wreck Blackbeard when on Shanks level of haki. Blackbeard doesn't even have Conquerors haki unless he has been hiding that he secretly has had it as well the whole entire time. The only problem is plot armor though... So who really knows what will end up happening besides Oda. They talked about Gol D. Roger being the absolute strongest around in his era except for maybe Rocks D. Xebec(who most likely also had Advanced Conquerors Haki like majority of his crew with a devil fruit as well.) Roger was devil fruitless with the strongest Advanced Conquerors Haki around the world... And that's literally all he needed to stomp everyone else out and claim that One Piece for himself.