Lightsabers: A Guide to Weapons of the Force (2018) states that Mace "nearly overpowered Darth Sidious, forcing him into a corner and holding him at blade point.": https://i.imgur.com/O0zF2n0.jpg
And in Secrets of the Jedi, Luke states that Mace "might have bested the Dark Lord in combat", had Anakin not intervened: https://i.imgur.com/Owjnrob.jpg
Registered: Jan 2020
Location: Chiss Defense Fleet
Vos was slightly above Dooku at best. A Dooku level fighter isn't contending with (let alone arguably besting) Sidious in sabers. And Asajj isn't skilled enough to help bridge the gap IMO.
Registered: Dec 2019
Location: Imperial Throne Room
Vos was slightly above Dooku at worst and I'm not sure why you think Dooku can't contend with Sidious when he was able to contend with Yoda (while exhausted) who is superior to Sidious in duelling.
Anyway TCW Asajj + TCW Dooku is enough to defeat Sidious, let alone DD Ventress + DD Vos.
Sidious knew that, should Asajj become any more powerful, the combined might of Dooku and Ventress could overthrow him. Star Wars Fact File Remake #067
Sidious and Mace are roughly equals so the team wins decently imo.