So when Red Mage was announced for Final Fantasy XIV I was super excited and decided to make it my main, switching from Summoner. At first, I was very happy with how they introduced the class to the game and I assumed the job would continue to grow and develop over time. Alas, in Shadowbringers I've only seen the job more or less stagnate to the point where I feel like i'm being pushed into playing Black Mage even though I love the aesthetic of the Red Mage. Oddly enough, I feel like the job can be improved in a few ways that would be fairly easy to implement and then in many others which would definitely take some work but I think would make the job more worthwhile.
Easy fixes
The biggest issue with RDM, in my opinion, is that it takes WAY TOO LONG to generate the mana necessary for the melee combo. I believe this could be very simply addressed by lowering the cooldown on Manafication to 55 seconds. To line up with this, I would probably also lower the cooldown on Corps a Corps to 30 seconds and Displacement/Engagement to 25 seconds. Some potency values might need to be slightly adjusted with this but the point is to make the job faster and more engaging while also slightly increasing its DPS.
Harder fixes
The other issues I have with RDM stem from its AOE abilities. The previous Stormblood version was abysmally boring and unfortunately the Shadowbringers version isn't much better. However, with the above changes in place I feel like SE could give RDM an AOE rotation who's function and flash are on par with that of the Dragoon. The first thing is to give the 50% proc of a second ability to Verthunder II and Veraero II. But instead of having them proc in the same fashion as the single target abilities, I would simply have them give an "impactful" buff which makes the next Impact generate twice as much black and white mana as it normally does. Then when you're at the prerequisite 80 black/white mana you should be able to do a true melee AOE combo in 3 parts which they can simply stack on the one button like they do in PVP...OR once you execute the first move of the combo, the single target combo moves transform into the AOE versions. I feel like SE could create some really beautiful sword attacks for this combo in the vein of Fleche and Contre Sixte but obviously they would have to make entirely new moves and animations for this so we'd probably not see anything like this until the next expansion but I'm putting it out there anyway.
Future changes
Finally, one thing I would like to see on Red Mage is a bit more white magic representation in its moveset. I certainly don't mean more healing abilities but Y'shtola, for instance, used some interesting conjurer-like abilities in her Shadowbringers toolset even though she seemed more or less a Black Mage and it would be cool to see things like this on the Red Mage since they are supposed to embody both Black and White magic.