Knull with about zero effort ripped Sentry in half, has an army of parasitic thralls in the billions, has a magical sword that’s gives no Fs about natural durability. Yeah I can absolutely see Knull cutting Doomsday into pieces. How? Well Knull operates on a higher level than Doomsday does and can alter gravity and use exotic powers that Doomsday has never encountered included trying a symbiotic infection to his genetic structure. He can possibly heal from this but it would take about a decade for him to return from whatever hell he goes to. Gorr would be a better fight imo.
I believe Knull doesn't have the Necrosword here and is also significantly slower than HP DD.
While ripping Sentry in half is an impressive feat, Sentry's durability is highly inconsistent - especially when you consider that Iron Man once busted his nose with a punch. Even at his most stable, Sentry lacks solid high-end durability showings. In my view, he's more on the squishy side, similar to the Viltrumites, rather than most high herald or trans-tier beings.
H/P Doomsday was mind-controlled by Braniac. And for some reason, Marvel has been pushing Klyntar symbiotes fiercely. Braniac mind-controlled H/P Doomsday for awhile. So at what point during that storyline would you consider that a win for Braniac? But H/P Doomsday doesn't need to be dealt "true death" to lose this fight. That's not the OP. Approximately the same lethal effects it had on Marvel Abstracts like the Celestials?
I mean... are you elevating H/P Doomsday over Celestials?
Superman has gotten his nose bled by similar force though. That isn’t any reason to question whether Sentry needed a durability flag. The only valid reason to draw on the conclusion that his durability had been compromised would be when Knull invaded his personal aura space by emphatically connecting with him on a deeper level, which is when he began manipulating the Void within Sentry who happens to be made of the same malevolent darkness that Knull represented. He then tore Sentry in two. Bob was assumed to always be operating at high herald levels, which spiked based on his mental state. Sentry’s soft underbelly is his neurotic nature, too much pressure and he might become paralyzed or Void out.
Why wouldn’t Knull have his standard issue weapon? All the same he would absorb a being like Doomsday into the fold by weaving his darkness essence into Doomsdays DNA. He attempted to do this to the Silver Surfer and would have succeeded in corrupting him fully if not for Ego’s help. The Surfer is immune to any disease. This was something different. It’s not always about brute strength alone and Knull wasn’t a slouch in the strength dept either. He has powers that ignore physical durability complete.
I got it mixed up with umbrakinesis (control over darkness). Good catch, I mistook his AOE in the fight with Surfer in Silver Surfer Black that I was convinced that it was a gravity attack.