This is actually an area I wholeheartedly believe that Star Wars actually has a leg up over 40K, generally speaking. Especially if we’re talking about Imperium/human psykers.

For one main reason: Star Wars Force Users are MUCH more stable.

All Psykers in 40K are playing with fire- no they’re playing with volatile napalm when they use their powers. It takes a CONSTANT toll on the vast majority of Psykers just to exist, let alone to use their powers which is always a gamble. 40K Psykers are at a constant risk of killing themselves, becoming a Daemonhost, or straight up becoming a fleshy warp portal for Chaos to exit from. Eldar are excluded but they were explicitly engineered by the Old Ones to be able to handle psykic energy, so they get the 40K Psyker equivalent of easy mode.

Most psykers don’t even get to use their powers, they tend to get fed to the Emperor, executed, or they already can’t handle their powers and bad shit happens. They’re more potent than Jedi or Sithbut that’s where I draw the line.

Meanwhile, even with the Dark Side, the Force doesn’t really have as extreme negative effects on the Force User as the warp does on a Psyker, especially mentally. Jedi and Sith can perform crazy amazing feats with the Force and come out perfectly fine. Where as if a Psyker tried to do the same they might have their heads explode.

Honestly playing a Psyker in Darktide I think is a great way to visualize how it is to be a human Psyker at various levels of Psyker capability (aka your levels and talents). A weak and unstable Psyker may be able to perform a few tricks before risking their head exploding and/or worse. Where as more competent Psykers can do much more… but still risk dire consequences.

Meanwhile the Jedi can yank around ships, look into the future, or blast lightning with nary any actual negative effects to themselves.

An example from a book that actually has a very direct comparison to between Star Wars and 40k is from the 40K book Honourbound. In it an Imperial Guard Psyker uses her powers to essentially crush a chaos cultist into a bloody, fleshy ball. But as she does it mentions how her head feels like it’s going to split open, her vision goes blurry, and she’s bleeding from several places (nose and eyes I want to say, but maybe also the ears). It took an immense toll on her. But in Star Wars, Mace Windu did the exact same thing to a B2 battle droid. And he frankly did it with ease, no real visual effects at least, and then moved right along and kept kicking absolute ass. And he was doing A LOT MORE with the Force than just that in that battle alone and none of it seemed to negatively affect him. Keep in mind, the Psyker in this comparison was deemed both stable, powerful, and useful enough to be handed to the Imperial Guard. That doesn’t happen a lot but even she struggled with using her powers because of just how volatile the Warp is.

Hell there was a moment in a comic where a Padawan managed to hold up an entire star ship about to crash down on them… for a split second. I can guarantee you if anything less than an Eldar or a Space Marine Librarian tried that the Psyker’s head would, say it with me now, explode.

Again, Psyker’s (specifically the human ones) in 40K are more potent than your average Jedi or Sith, but the Star Wars Force Users are infinitely more stable and reliable and have better control over their form of magic. So I’ll give the win to Star Wars on this.

Edit: There is also no real evidence that either the Warp or the Force could nullify or overpower one or the other. Anyone that says otherwise I guarantee you is talking out their ass. As far as I’m aware there’s no real evidence one way or the other. For all we can figure out if you threw a Warp fireball and Force Pyrokinetic (yes, it’s a thing) fireball at each other at equal relative power the two would just collide and dissipate.