At this point, it seems like Mind over Matter exists only to enable Eldrich Battery. The number of builds where it makes sense to actually build for mana has been dwindling with every patch since its peak in Delve. I think a lot of this has to do with the new reservation skills that were introduced, but it's also been affected by unique item and Ascendancy balance.
In Patch 3.5:
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Energy Shield Recharge is no longer interrupted by non-damage changes to your Life or Energy Shield, such as when you spend your Energy Shield on skills via Eldritch Battery. Eldritch Battery now causes you to have 50% less Energy Shield Recharge Rate.
EB (without MoM) gets a default 10% regeneration rate! Compare this to Mana's 1.75% regeneration rate which has to be scaled with major investment. Now you can reserve all of your mana AND spam your skills with significantly less investment.
Indigon is nerfed, hurting one of the main reasons to build for mana. Personally, I wasn't opposed to the idea of the nerf because of how ridiculous Indigon was in Delve, but the nerf was too heavy handed. The juice is no longer worth the squeeze, especially when the juice is capped but the squeeze is not.
Betrayal also introduced The Devouring Diadem. To make matters worse for Mana vs EB, this helm removes the significant point investment some builds would have to make to reach EB, gives a huge amount of recovery with recharge/instant heal, and then gives EB builds room for another reservation skill, as if mana builds weren't already lagging far behind in this regard.
Speaking of reservations, 3.6 introduced Zealotry. While before some builds like lightning casters could justify using a Essence Worm with their 1 damage aura and forgoing other weaker reservations like Heralds, the introduction of another big damage reservation that could be slotted into almost any spell build made this option less appealing. Hatred was also changed to include a more multiplier for cold damage, so yet another build has less reason to have unreserved mana.
3.6 also included huge buffs to energy shield recovery and nothing but nerfs to mana recovery. Casters got energy shield leech all over the tree, and a powerful support gem giving both leech and damage. The Inquisitor Ascendancy also received a large amount of ES regen, for even more synergy with EB. Meanwhile, one of the strongest forms of mana recovery, the Inquisitor's whopping 6% base mana regeneration, was replaced with a measly 15 mana/s!
Things didn't get any better in 3.7. We got another insanely powerful and generic reservation in the form of Flesh and Stone, with its blind aura and 11% less damage taken. With Aspect of the Spider costing a mere 20c I can't think of a single build that couldn't easily reserve all of its mana with useful auras. Mana leech for spells got removed for Warlord's Mark. Wicked Ward is now on the passive tree.
I was really interested in making a build around the new Agnostic keystone, but the opportunity cost of losing all your auras in addition to the cost of significant investment into mana makes it incredibly hard to justify. The only builds I can think of that can reasonably take advantage of scaling mana are ice nova, with its synergy with the absolutely busted Pledge of Hands, and Mana guardian, which just uses mana as an alternative way of scaling energy shield. Something needs to be done to make mana more worth using, there are so many interesting items and interactions that are shelved because of the issues that mana based builds have right now.
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