The issue with this (and your other one) is that you have to use a unit for stats to achieve it, and that is not worth it on forces. Forces already have their unit space extremely limited, so having one for stats alone is crippling. Force using melee will pretty much always have battle unit, smartlink, and v801 on regardless, leaving only 1 slot for v502 / cures / trapsearch / resists/ etc. (also v502 does not affect demons, it only affects hell/paralyze/freeze/confuse specials; smartlink on the other hand is worth more than a c/arms even at only mech range, it's basically a mandatory unit). Making the armor a actual part of the build is questionable when you could be using armors like kroes or sweetheart which much more significantly boost your stats overall.
Being able to max dfp/evp on fomarl is completely irrelevant as not only are those stats are basically just as weak or weaker than mst is, raising her already low evp won't make any difference at all, and she has the naturally highest hp of the forces anyway as an actual defensive stat. Fomarl can max all her important stats regardless (ata, lck, atp, mst) without having to rely on neutron skin, and fonewearl isn't going to be able to use it to substitute needing 2 mags really.
If you actually know how the tech formula works, mst is actually kind of a joke in what it really does for your techs (it's the least significant thing in the tech formula), the only place it's actually sorta valuable for is resta healing (only 2mst for 1 heal on resta, but a whole 5mst for 1 damage on tech before boosts and resists are applied, so effectively less gain than that usually), the 10ata from kroes or the ~50-200atp from a sweetheart is far more valuable than the mst from neutron skin for the most part.
It is a very good armor still, not only for a low level force needing extra mst to equip support gear like glide, but also at high levels when you want a more support focused armor to give you some extra resta range and power on fonewm/fonewearl/hunewearl/ramarl or even humar/ramar, but the having the extra mst, whether it be from wearing neutron skin or from not wearing a mind mag in a 2mag plan, is not what is going to make or break techs being useful in casting role, that isn't nearly as important as just equipping the right techboost gear (e.g. if in ep4, I decide to help team by nuking down lizards, simply equipping hylian + pwand/quasar/pbridge is enough without having to switch to mind mag for it).
I only touched on a few of the nuances on how certain stats work/don't work and maxing principles, but I hope it helps explain things a bit anyway.