150 is too high. I imagine Doom Slayer to be a clunky, hard hitting character like Bowser and Ganondorf. Hell, even 100% is pretty high considering the percentages those guys KO at, but 100% is the standard for instant KOs with Great Cave Offensive, Death's Scythe, and Zelda's Final Smash.
That all depends on the damage output of the Slayer to begin with.
Hard-hitting, most definitely. But clunky? Far from it.
I had a similar Glory Kill concept for my own, though I put my own threshold at 150 damage. While it
is rather high, this is more-or-less made up by the fact that the Doom Slayer's attacks either hit really hard or really fast. Mostly both, tbh.
Also, would anyone be willing to post suggestions for throws/Glory Kills? I've been thinking of giving him multiple animations for each direction, and it'd be cool to see what people can source/come up with. Perhaps there could be a few fighter-contextual throws, like the Slayer taking Samus'/Mega Man's arm cannon and shooting their heads with it.