Currently, Souleater seems to recover a random amount of the damage dealt (anywhere from 1-100% of 288 or 422 with DA?).

RNG will even it out to an average potency of 144 or 211 with DA.

The cure potency in 5.0 is a flat 300, which is a buff compared to these two averages.

It's obviously got the least of the self heals but that's always been the case, because using DA+Abyssal Drain twice is sacrificing your entire ability to AoE for a period of time.

In practice, have I struggled with self-sustain on DRK beyond being forced into Grit to do it? No, because the combination of cooldowns, stuns, souleater, very rarely DA+abyssal, resolve any problems. Since in 5.0 Souleater's heal is buffed and Abyssal's heal doesn't drain MP, my self-sustain should be way better.

I mostly use DRK in pre-70 content, so at 70 there is The Blackest Night too which absorbs damage totalling 25% of maximum HP. Technically that is self-sustain and could help you survive when combined with Souleater and Abyssal.