Soul leech as really bad damage mitigation mechanic for warlock for many reasons.
First and foremost, warlocks idea was never about shields it was about regain your health via Drain life, health stone, siphon life ETC. Before legion.
Damage mitigation was part of spells like demon armor and fel armor.
- Demon Armor
- Level 8 warlock ability
- Instant cast
- Protects the caster, increasing armor by X, and increasing the amount of health generated through spells and effects by 20%.
Only one type of Armor spell can be active on the Warlock at any time.
- Fel Armor
- Level 38 warlock ability
- Passive
- Increases total health by 10% and the amount of health generated through spells and effects by 10%.
Shields was never your baseline defence spell.
This why, dark regeneration - a talent that was introduced in mists of pandaria was more popular than soul leech that was introduced in same talent row
- Dark Regeneration
- Level 15 warlock talent
- 2 min cooldown
- Instant cast
- Restores 20% of maximum health over 12 sec to you and your pet, and increases all healing received by 25% for the duration.
Right now, warlock desing is stands against warlock class fantasy, and warlock legacy.
We need dark regeneration instead of soul leech, or demonic armor being made a baseline spell for all specs, and soul leech thrown away or made some pvp talent.
Soul leech mechanic - deal damage to gain shields in not useful in current gameplay meta.