We see in the ROTS novelization that it takes time for Mace to submerge himself in Vaapad; the metaphysical superconducting loop of Vaapad is neither instantaneous nor limitless as demonstrated by the source material; Palpatine, despite enormous disadvantages, took the offensive and drove Mace back into the greater office and Mace, even in the very depths of Vaapad, could only match Palpatine's power (never surpass it).
Mace is unquestionably the more skilled duelist (though Marek is a Juyo master [making him a "high-end master of multiple forms" according to Fight Saber]), due to his prodigious physical attributes, shatterpoint charism, and more extensive dueling/combat experience.
But though Windu is considerably powerful in the Force (something for which he is routinely underestimated), Starkiller's feats dwarf Windu's by several orders of magnitude. Early!Starkiller struggled immensely with Shaak Ti, a Council member who, while enormously skilled, was definitely Windu's inferior.
Later!Starkiller, on the other hand, handily defeated Darth Vader and "tanked" Emperor Palpatine's Force lightning (something Mace Windu didn't do).
If this is early!Starkiller, he probably loses due to Windu's superior skills as a swordsman and not inconsiderable talents as a Force user. Later!Starkiller, on the other hand, enjoys a tremendous advantage in Force powers and I don't believe Windu will have the chance to submerge himself in Vaapad to steal a win.
Originally posted by SlightlyFlaccid
Later!Starkiller, on the other hand, handily defeated Darth Vader and "tanked" Emperor Palpatine's Force lightning (something Mace Windu didn't do).
And the evidence would show Palpatine's Force Lightning being considerably more powerful by the time he fought Starkiller as well.
Jinsoku Takai
Really? Mind expounding on this?
He instakills Jedi in Dark Empire, incinerates dark side mages in that one comic in which Vader duels a resurrected Darth Maul, and annihilated ~50 stormtroopers in the comic Betrayal.
But, if I remember correctly, Palpatine's lightning disintegrated a Sith wyrm in Sithisis, so I doubt it increased dramatically.