I wanted to preface this by explaining a bit about where I am. I started playing FFXIV back around 2020, and I started off with Thaumaturge so I could go into Black Mage. The reason was simple, I just wanted to be a wizard with a big hat.
Ever since, Black Mage has been my main! And I've loved it, even now where it feels a bit rough. I took a break from last April to now, where my level was only 80, so miraculously I actually missed all the Ice Paradox stuff I've seen people mention. So a turret I was before, and a turret I remain.
Even now I'm not max level, I'm still finishing post-Endwalker. But even I can see the trouble Black Mage is starting to experience with encounter designs. While I'm not one to care too much about optimal DPS, it does feel like I'm having to pause a lot or reset my rotation just to keep up with bosses. This is partly on me forgetting that I have Triplecast when I need it, but other times it's simply that enemy attacks are too oppressive.
I've seen a lot of threads talking about improving Black Mage's mobility, with some responses being dismissive as doing so would homogenize the class with other casters. So I have the following proposal:
What if we could negate Vulnerability Up?
What if, instead of having to break your rotation to keep up with ever-faster bosses, you had a passive that gave you some leeway? Obviously you never want to get hit with attacks in the first place, but the biggest problem really is Vulnerability Up since that will just compound the damage.
My proposal is thus: Somewhere from 70 to 80, we could add a Trait that gives you something like "Transpositional Barrier," or some similarly cool name like that. Any time you enter Astral Fire or Umbral Ice, that barrier buff activates and gives you 3 stacks for 30 seconds. During that time, if you get hit with an attack that causes Vulnerability Up, a stack is expended to negate that status.
Ideally you should never have to solely rely on this trait. But I think it would benefit Black Mage and allow it to remain as a turret caster in a lot of cases, because you could weigh the cost between taking damage or finishing your cast. It's probably not the most perfect idea out there, but I thought I'd share it and see what others who are more competent at Black Mage than me think about it.