That's the thing. we did just fine before with how the kit was. I raided back in Endwalker, and I'm currently progging the Eden Raids synced on Black Mage. Movement wasn't nearly as big of an issue as it seems if you just take a moment to learn what you're capable of, and give it a couple tries. It does take a bit more to master than a phys ranged, I'm not denying that. What matters is that you've got what it takes to clear the fight without being a burden to the party damage wise. We're given so many tools to enhance movement that some people even say that Black Mage is more mobile than Red Mage (Which might be true in situations with long sustained movement, but not most of the time.) Hell, even now I barely feel like I'm pushed to the brink of my mobility kit. Valigarmanda was the only fight where it felt like I actually needed the extra movement from instant Paradox and Firestarter. Most of the time in Light-Heavy-Weight, I'll sit at two charges of Triplecast and not even notice because of how little movement we need to do in those fights. I still need to spend a ton of Xenoglossies to avoid overcapping rather than movement.
I'll agree that the leveling experience needs a bit of a look-over, but I don't really get what's so hard to understand about Black Mage for new players. As long as you're not trying for 100% uptime on every fight your first time through (and if we're talking about new players, they're not.) It's actually a very easy job to play. You don't even need to think about that Enochian timer until you get FireIV at level 60. Before then, you have all that time to learn and master your GCD timings, How and when to swap to Ice phase, and back to Fire, how to keep Thunder up at all times, and maybe even how to weave if you're really good.
I'm just speaking from my experience though. My first 50 levels were as a Black Mage, and it's always been a step or two behind Scholar until I got to level 90. Personally, I think the real solution is to make an in-game way to learn how each class works in their fundamental rotation. Something like Hall of the Novice, but for each class. It shouldn't try to teach optimized openers or anything, that's up to the community to figure out. But stuff like "Use Despair when you've got 2399 or less MP because it hits harder than a FireIV, but takes up all of your MP as long as you have at least 800 to spare." or "Use Blizzard 3 to swap from Fire to Ice because with that one spell you'll go straight to Umbral Ice level 3. Same with Fire 3 from Ice to Fire, using it will instantly put you at Astral Fire 3 for no MP cost if used under Umbral Ice."
Teach people how to play better rather than making the game easier to compensate for people who don't know how to play. Remember that if a player wants to improve, nothing can stop them. If a player doesn't want to improve, nothing will help them.