I don't think the forcegrip would be too much help for Vader. Doom had his body casually ripped apart by Beyonder and still magaged to beat him. And allowed Purple Man (a psychic more powerful than Xavier) to attack mind directly, and it didn't even phase him. I think Doom can handle Vader in a straight fight, although it won't be easy.
(Oh, and y'all left out that he also beat Silver Surfer, Galactus, and the Freakin' WORLD!! Just incase y'all forgot😉)
why do people keep saying "doom beat THE WORLD!!!" Umm.... how many planets has vader conquered? And i don't mean with the imperial army backing him either... Oh, and the "force grip" used to "choke" people isn't actually draining them of oxygen. Its the force sapping the very life essense out of them.... nothing can live through that, litterally... (unless of course they can combat against the force itself... aka one with force powers... aka a jedi of some sort, NOT a telepath/psychic)
The lightsaber would NOT help Vader here, basically the only thing Vader has is the Force, which I'm pretty sure Doom can find a way around. Just because you can't think of a way, doesn't mean it's impossible.
Ever hear of Ironman's energy displacement/converter field? It's on the surface of his armor, and it absorbs all energy, and converts it into power for Stark's suit. Guess what Doom can make? Hey, what's that lightsaber made of again...?
I don't underestimate doom.... but there have been many in the star wars universe to use magic (NOT the force). They were no match for vader. Then there were those who used both the force AND magic... again, no match. I'm not saying doom's magic isn't stronger than the magic that vader (and others) have faced, because it most likely is, i'm just saying that magic, nomatter how powerful, isn't anywhere near as powerful as the very substance of existance.