Pretty sure Mifune is quite a fair bit stronger than anyone on Team Kakashi except maybe Yamato. Early Shippuden Naruto wasn't all that great and even Sai seems more of a threat IMO.
Mifune's speciality is blitzing the opponent before they can activate their jutsu but he can't do that to all four at once. Yamato can grow wood out of his body without hand seals and Naruto can use rasengan and Oodama rasengan without hand seals. Neither will probably hit Mifune in a 1 VS 1 though. Sakura isn't much of a factor in this fight since she has to come very close to land a hit but Mifune's sword has a much longer range than a punch from Sakura. Not to mention that Mifune is far faster than her. She could still be of use when it comes to healing and as a distraction though.
The sheer quantity of Sai's ink beast could potentially overwhelm Mifune because after all, he'll be busy dealing with wood style from Yamato and shadow clones from Naruto. Also if Sai manages to go airborne and create ink birds for other members in his team, Mifune won't have a way of attacking the airborne opponents while his opponents can launch all sorts of long range attacks on him.
Yamato, Sai and Naruto are all users of clones so Mifune will be heavily outnumbered.
So Team Kakashi wins mid difficulty.
