The 1st two cases mean things are probably bad enough that I think the extra HP and accuracy would be worth more for a war to turn into a sudo tank for a while than bits of evasions
It's not "just a bit of MEVD", Magic Accuracy works in a very similar way as melee accuracy with it having a significantly lower growth rate. 1 MEVD = 0.5% resist rate, thus -169 MEVD is -84.5% initial resist rate. When coupled with barspells, and later carols (higher level content) or attunement, you can effectively mitigate status ailments. If a set of mobs does amnesia, then you stack 230 fire resist from Barfire with Baramnesia (seperate check) and normal MEVD from gear and suddenly amnesia happens less frequently and when it does get through, will last for less time due to failing subsequent resist checks.
If a certain set of mobs like to spam TP moves with additional effect stun, like say every god damn thing in Dynamis D, then Barthunder and normal MEVD is an immense help in reducing that effect.
I don't give much credit to meva because if you're fighting something dangerous enough then you probably not evading much.
https://www.bg-wiki.com/bg/Magic_Evasion
Then you don't understand how MEVD/MACC works, probably don't bother with barspells either. For a long time a bug enabled GEO to exploit MEVD's lower scaling to completely shut down status ailments on all content. They also allowed mages to nuke unresisted with minimal buffing by exploiting the same effect but in reverse. Magic Accuracy scales at a much lower rate then physical evasion (~30 per level after 99) causing monsters to have several hundred less MACC then they do normal accuracy, which places the
vast majority of fights within the range where MEVD stacking is useful.
All players have 373 base MEVD at level 99, gifts give WAR another 36. Then gear adds more MEVD and finally elemental resists get added. As long as the player doesn't do something stupid like wear Arke or TP in Argosy they can hit past 50% initial resist rates with just a barspell.