You in multiple occasions said he cant do that without amp and this is neutral ground. Sion is considered to be tiers below Anakin so even if someone wanted to make an argument for Bane against Plagueis, the mismatch that is Anakin vs Sion guarantees team 2 the victory even in the eyes of the biggest Bane fanboy
Darth Plagueis is likely to overwhelm any combatant [1 on 1].
However, argument is about Darth Sion since he have the capability to resurrect himself after being struck down. He may not be good enough to contend with any individual in opposition [1 on 1] but his virtual immortality can prove to be a problem.
Melee contest
Team 2 have decisive advantage in this type of contest. While Darth Bane may be able to hold his own against any opponent from Team 2 [1 on 1], Sion is lacking in expertise in this area. Therefore, once Sion is down, Bane stands no chance and will be quickly overwhelmed.
Force powers based contest
Team 2 again have decisive advantage. Bane may prove to be a match for Anakin Skywalker but he doesn't stands a chance against Plagueis. Sion is once again lacking in showings in this area besides his virtual immortality.
Plagueis can certainly make room for overwhelming both Bane and Sion with aid of Skywalker. And once Bane is down, Sion can be effectively contained.
All-out
Team 2 still have edge. Though difficulty of the confrontation may vary depending upon who confronts whom.
Scenario 1
If Bane confronts Skywalker, he (i.e. Bane) can win. However, Plagueis is likely to overwhelm Sion quicker or multi-task to help Skywalker in overcoming Bane while keeping Sion at bay. Team 2 will triumph nonetheless but Plagueis may have to exert much more in this scenario.
Scenario 2
If Bane confronts Plagueis and Sion confronts Skywalker, Team 2 may prevail quickly in this scenario.