You're probably correct, about the things not likely to be changed, but at the same time UO's Pvp has died significantly Since the SA release, more so once throwing & mysticism have been realized how good they are compared to other skills.
I'm not one for blaming anyone but... look where we're at now. I don't want UO to turn into WoW, EQ1/2, Rift, Lotro, & pretty much every other MMORPG out there.
Which is why I am trying to bring this stuff to attention now, before it's so wide-spread it would be even more devastating to change it down the road when people become more use to it (just like the tactics/special toggling thing, It hurt UO so much another thing like that would likely kill it off).
I think a change of Casting Focus would be fair to give you a chance to restore mana or stamina when getting hit,(remaining capped at 12% as it currently is) instead of allowing a mage to cast without being interrupted while not in protection.
This isn't only about dueling by the way, I'm just using "Dueling" as an example because it's an aspect that almost doesn't exist anymore (because of skills being overpowered) I for one have no interest fighting overpowered skills because I would prefer to play something involving more Player-Skill, (Pure-non-focus-mage) instead of a mixture of both "P-S/RNG".
Casting focus & Poisoning not only effects dueling/pvp in a negative way by adding an RNG Chance to things it also puts all Melee/Ranged dexers (mostly melee) at an even greater disadvantage.
If anything, giving a passive Resistance/immunity to Poisoning should be exclusive to dexers. Mages already have the fastest ways to cure, thus they shouldn't benefit from it, or it should be removed completely.
They could change poisoning to give the same chance to "Resist" poison as Resisting Spells does, or stack it with Resisting spells to give a 5-10% better chance of resisting it. Just remove the free cure... potions aren't good enough? I just don't see why some of these changes were made (It sounded good to me too reading the patch notes it just so happens it's not what I thought it was going to be like.)
Unfortunately, Player-Skill & Diversity to me, are two things that are unique to UO, Their the first things I look at when I try other MMORPGs. The Current track seems to be straying away from the "player-skill", and moving towards the "RNG" (straying away from the "player-skill" is never a good thing). If I wanted to play games where RNG & Items are the primary factors that decide who wins I'd play WoW.
In UO you can kill someone when you have no armor on. You can pvp effectively while suffering from stat-loss. These things involve pretty precise timing on both Defense & Offense, but it is infact possible to compete with players while at an item/skill disadvantage. Such is not the case in most other MMORPGs.
