I don’t know what the solution is with current game design of M+
Big pulls are a nightmare while the warlock is constantly moving, therefore relative nameplate positions change.
Sure addons / profiles make it easier to see important casts to interrupt or targets to focus DoT… but you need accurate cursor control. Something that only comes with the frustration of practice.
What makes it worse this season for everyone is some mobs being immune to AoE stuns - they just keep casting, or if can’t be stun/interrupted, go right back to spam casting anyways and your relatively long Spell Lock / Shadowfury (with a stupid cast time) is ‘wasted’ even the times you didn’t double-interrupt to put it on CD.