I assume you talking about Unstable Core as it only debuff morph now.
In compare to current - its base damage decreased since last 25% nerf and deal now 3 times less damage while cooldown increased from 0.750s to 1s. So it deal exactly same damage as ordinary single-target DoT now, can tick once per 1-2sec with CCs but only if enemy attacks. And since it cant be refreshed anymore - it easy to avoid CCs.
P.S.: And Unstable Core no longer has magnetic bomb explosion that couldn't be avoided and was equal in damage to Curse.
Skill dont reflect/absorb attacks for like 2 years, it just proc moderate damage on enemy. And old Total Dark had healing proc as morph effect every time damage proc was proccing. But next update it will no longer able to heal and deal damage so Unstable Core wont have this defensive effect that was allowing to go offensive when bubble on enemy coz you was healed when enemy attack you.
In exchange of loosing this defensive capability it got better but delayed CCs.