Dodging the grab is unreliable, even if you dodge towards the tentacle arm. Dodging experience should be consistent. Consistency issues remain a plague on the core gameplay experience.
You can still get damaged by other enemies and fire pools whilst grabbed. This is “mainly” caused by damage over time attacks / chain attacks which began before you were grabbed: gunner bursts, flammers, fire pools, but also stuff like kicks.
Getting trapped in the ceiling in any hallway or elevator or low room because it grabbed you is definitely broken and should have been fixed eons ago, but in as far as I can tell the spawn arm actually has to be physically spaced to dodge. I can always reliably dodge it timing 1s after the animation of the grab begins, but if my only movement area is somewhere still ranged by his arm I get grabbed. That seems fine to me.
And the absolute worse for it is in monstrous specials, when you get puked on inside its tentacle and then grabbed the instant it launches you into more digestion. So much not gameplay not had by one player. But the Nurgle beast badly needs this fix too, like when it rides over some fire with you inside and you don’t even live to escape. That’s a bit insane of a punish.
Honestly I think the fix would be to just make the player “invisible” to all enemies except the enemy that grabbed you, so all enemies break off. If you’re in fire, well that’s just unlucky.
Another solution could be to make the player invulerable to all sources of damage execept for corruption. Since the Chaos Spawn/Beast of Nurgle grabbed attacks are both corruption based.