Let me start off by saying, I am not asking for a revision to the suggested nerf for necropotence. Instead, I am proposing a slight change to how the 5th set bonus of necropotence works mechanically.

Current proposed change.

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(2 items) Adds 1095 Maximum Magicka
(3 items) Adds 1095 Maximum Magicka
(4 items) Adds 1095 Maximum Magicka
(5 items) While you have a pet active, your Max Magicka is increased by 3150.

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Suggested proposed change.

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(2 items) Adds 1095 Maximum Magicka
(3 items) Adds 1095 Maximum Magicka
(4 items) Adds 1095 Maximum Magicka
(5 items) While you have a pet active, you get a buff which increases your Max Magicka by 3150 for 10 seconds. The buff is refreshed every time it ends. (Much like how Spell-Power Cure 5th set bonus but with a 100% chance of activation.)

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Objectively, this overall DPS from the current and suggested proposed change is similar, but my suggested proposed change dramatically helps Restoration/Destruction staff based set users, allowing ranged magicka necropotence users.

Specifically, this helps those who wears a 2 piece monster set, and 2 5-Set bonus sets via weapon swapping.

For example, Consider the following.
2 piece monster set.
Head - Infernal Guardian
Shoulder - Infernal Guardian
Necklace - Necropotence
Ring - Necropotence
Ring - Necropotence
Gloves - Necropotence
Chest - Spell-Power Cure
Breeches - Spell-Power Cure
Belt - Spell-Power Cure
Boots - Spell-Power Cure
Weapon 1 - Necropotence Destruction Staff
Weapon 2 - Spell-Power Cure Restoration Staff

With the suggested proposed change above, even when switching to the Spell-Power Cure restoration staff, the player can still retain the Necropotence 5 set bonus for around 8 seconds or so.
Not exactly a boost, but still a very useful change for necropotence, allowing this set to work well with other proc based boost sets.

Note that the nerf change is still there, but how the bonus get applied opens a bigger field of sets which can work effectively with necropotence.