teschnei asked for feedback, so I thought I'd kick off the thread and get that rolling, and give the players a better idea of what was actually done. Think of this as a sort of "patch notes" for a hot button issue. You did it in 40 lines less than I did, which isn't surprising at all

Obviously, under the old system, HNMs and Sky Gods gave mages a -130 to -150% magic accuracy penalty, so anything is an improvement when you literally can't win. The current system is built on the wiki formulas, with no level correction applied. Level correction is unknown (if it exists), so that's probably for the best.
Looks like dark/elemental seal was changed from accuracy * 2 to accuracy + 256. The players technically lose there, but to be honest, both situations led to capped acc unless you were something like a L60 BLM nuking an HNM. It will be a bigger buff for lower level BLMs, however.
The staff bonus threw me for a moment, but once I understood it I was okay. That'll have to be fixed if staff is ever changed.

I honestly didn't look at Skillchain burst acc, and I'll take your word for it. Either way, nothing changed here (literally).
Individual elemental resistances were added, which was missing before. That will make things more interesting.

Magic evasion isn't touched, and I don't blame you. It does mean that there is a steep jump in magic evasion from 83 to 84 (263 -> 299,) but we have too little information on mobs to approach that, really.
Sixteenth resist... I never found any information on it, but I didn't go looking. Maybe it was removed in the last two years. The odds should stay pretty narrow unless you're up against a huge accuracy deficit, and I'm not a BLM, so no sweat off my back.
Final spread means that a 75 BLM/RDM with 96 INT, 276 Elemental Skill, an HQ staff, and 9 MAcc will have to "roll" above the following percentages to avoid the resist against a L88 HNM, without calculating individual elemental resists:
2.69% 1/16
6.64% 1/8
16.4% 1/4
40.5% 1/2
I'm not a BLM, I have no idea if those are accurate or even close.
Drop 5 INT and go up 19 Elemental Skill, and it becomes:
0.7%
2.4%
8.4%
29.0%
All in all, I think this has made HNMs possible for BLM, but not necessarily easy. Information from a career BLM would probably be more welcome than my analysis. If anyone wants me to plug in the numbers and see what comes out, I just need elemental skill, player's INT, target's INT (I can fetch it myself if necessary, just name the mob), MAcc gear, and target's level or magic evasion.
Edit:
Oh, on enfeebles, if anyone doesn't already know it. It should be sixteenth, eighth, quarter = resisted, half = reduced duration, otherwise it sticks. I haven't checked to be certain, but I'm assuming Darkstar already does that.