Well, after the events of Ep3, The Emperor hunted for ancient sith knowledge and spent a great deal of time improving his powers and techniques, even making new ones up as he went along. He taught some to Vader, so Vader should SOLO the three Jedi Masters at the same time. I mean, if you are going to use include the Force Unleashed story ( ughhh ) by that time, Starkiller could bring down a Star Destroyer by force pulling it and he only barely managed to beat Vader. The gap between Return of the Jedi Vader and Ep3 Jedi masters is massive.
You can't say for sure. Vader and Sidious were supposed to be the two most powerful force users of all time. Mace was dumb enough to not see Anikans attack coming, and Sidious fended off FOUR...count them...FOUR Jedi Masters with enough skill to coax Mace exactly where he needed to be and end the fight just as Anikan ran inside. Yes, Darth Vader SOLOS all of them. His power drastically increased after the events of Episode 3. None of the Jedi masters prior were even remotely close.
Wait, what? Seriously? Vader solo? Nobody is soling here, and Vader gets stomped if he tries to solo. And LOL at Tenebrous being a bonus. Tenebrous is stronger than Vader.
Starkiller could bring down a Star Destroyer by force pulling it and he only barely managed to beat Vader.
For the billionth time, Galen Marek did not pull down a Star Destroyer, it was already falling and he merely guided its trajectory to the Junk Cannon.