People are getting confused between Zoro's dream and Mihawk's title. All you've done is confirm that Shanks is a swordsman; was Big Mom ever referred to as a swordmaster? King? Pica? These are names commonly used to argue that Shanks is not a swordsman when he literally has the title of master swordsman.
Mihawk's title has been translated as World's Strongest Swordsman. Zoro's dream may directly translate to being the strongest Great Swordsman, but Mihawk's title has been translated as being the strongest swordsman in canon material. Sekai Saikyo no Kenshi.
That puts him above everyone who is considered a swordsman; and if you're a swordmaster, you are absolutely considered a swordsman. All you've indicated is that Shanks isn't included in Zoro's dream, but Zoro's dream =/= Mihawk's title.
Zoro is a master swordsman stronger than Vista and Ushimaru, two people considered Dai-Kengo. But Zoro is still a swordsman. As such, he would be included in Mihawk's title of Sekai Saikyo no Kenshi. And so is Shanks.