He beats Danzo, Tobirama, Minato and stalemates Mū. Gaara does not beat the 2nd Mizukage or Mū. He beats Tobirama, Minato and Itachi because he is a damn good counter to them.
Danzo beats 2nd Mizukage. Baku to suck up the mist which causes the genjutsu, followed by Baku enhanced fuuton to cut the clam in half. Joki boy can be cut apart with fuutons. Mizukage is put under a brief sharingan genjutsu then followed by a shunshin and wind chakra blade to the heart. And Danzo gets 10 full minutes of immortality in which he can remain purely on the offensive and wear down the Mizukage without having to worry about defending himself.
Mizukage loses to Tobirama. He uses his wide-scale suiton to locate the clam and blows it up with GK. Mizukage's attacks can be evaded completely with FTG, and GK also finishes Joki Boy and the Mizukage himself. Shadow clones or Edos to deal with different attacks on different fronts. Without Edo Tensei though, I think Tobirama would lose.
Upon further consideration, I agree that Minato loses.
Exactly, Mu and Mizukage stalemate just like they did in canon. Except 2nd Mizukage is much higher than Mu on OP's list.
(Jiraiya beats 2nd Mizukage too)
Gaara beats 2nd Mizukage, more or less like he did in canon...sand sensing detects the clam which can be sealed away with a Grand Sand Mausoleum. Joki Boy can be stalled while Gaara uses his Third Eye to seek out the Mizukage (who by the way is significantly weakened when he uses his steam clone.) Mizukage is then sealed away like he was in canon.
Gaara beats Mu. Invisible sword attacks obviously won't work so Mu will need to become visible in order to prepare jinton, and Gaara would notice him instantly by literally keeping an eye out for him with the Third Eye. He is also capable of detecting Mu via sand sensing. He can mix himself in with sand clones so Mu won't know which to target. Gaara just needs to use several massive sand tsunamis with large ranges and eventually he snags him and crushes him in a sand coffin.
Exactly, Gaara beats two FTG users and an experienced MS user. That should hold some merit.