Really, it just needs Paradox to get it's cast time back, and Sharpcast with old Thunder back (and by proxy, the non-guaranteed firestarter procs)

Flare star is servicible in it's current iteration. I don't hate it, but it's just underwhelming. If I had to design it, I'd just make every FireIV you use that doesn't use an Umbral Heart give you an Astral Heart, which occupies the same spot in the gauge. Then make Flare Star only available at 0 MP, and have it's power scale with how many Astral Hearts you have. It means losing one FireIV isn't that big of a change to the rotation. It makes Flare Star feel more contingent with the rest of the rotation, giving it a proper place as opposed to "well, the counter got to 6. time to use the thing that I can only use when the counter gets to 6"

I wasn't a big fan of Thundercloud before you got enhanced Sharpcast. Having Sharp be on a 30 second cooldown with 2 charges made the skill actually feel good to use. It wasn't perfect, but it added a necessary level of variation to your rotation. It wasn't entirely obvious that you could/should play like this, but you were meant to use Sharpcast some time before your next Thunder in such a way that you don't use Paradox first. Otherwise it'll turn into a Firestarter proc instead. If I had to design something to fix this, I'd just make Sharpcast have no cooldown, and instead just cost MP. This is a rough idea that I'm not too certain about numbers wise, but I think it'd be cool if you just spend 400MP to cast Sharpcast (maybe have zero cost when under Umbral Ice.). This way, you only get one per fire phase, or else you lose a cast. But even if you've got a long Fire Phase, you can still just use the Thundercloud proc without Sharpcast, and leave it up to chance whether you get a free proc. Plus, if you know you're not going to need Sharpcast this Fire Phase, you can intentionally use it for the Firestarter Proc, making that an actual mechanic instead of a fail condition or RNG exclusive mechanic.

It would have a similar, but much less severe issue than what we currently have now. Where if you have a particularly long Fire phase, your Thunder can just fall off before you phase shift, and you have no way to put it back until after you finish Fire Phase. But instead with my proposal, you would just use it anyway, only without Sharpcast, which leaves you to randomness on whether your next one will be hard casted, and half potency. It's still a failstate, but it doesn't throw everything out of whack like it does now.

Paradox being instant cast throws off the entire timing of your Fire Phase. It's baffling that they decided to do that. Having the Enochian timer start 2.5 second earlier means you can only get three FireIVs and a Despair in your latter half Fire Phase, but you still only get four FireIVs in the early half because of FireIV's longer than GCD cast time. I find myself and many others using Paradox for movement, and not having enough time to actually finish the Fire Phase normally because of it. I think that's why they made Firestarter a guaranteed proc, but now it just feels like they gave us too much room to make mistakes that we don't even need most of the time. They wanted to kill non-standard, but now Transpose is part of the basic standard rotation. Good job guys.

Having your Movement and main rotation be separate made you think about what to prioritize. If you only need one or two GCDs of movement, then you're fine to just use a Xenoglossy and Thunder. If you need three GCDs, or you need two and have already used one this fire phase, then you use Xenoglossy and Swiftcast. For heavy movement, there's Triplecast. I will regularly find myself sitting at 2 triplecast charges for extended periods in a fight because most of them don't require anything close to as much as we have.

We made do before by being smart and planning things properly, now I'm optimizing my movement by just guessing correctly in a week 1 savage blind prog. The only fight in Dawntrail that feels like it actually pushes us in the kind of way that Anabaseios, or the Endwalker EX trials did is Valigarmanda EX.