Well, no, I do think the skill floor is getting a Flare Star each astral cycle. I just think the job gives you the tools to do that reliably if you don't try to spend those tools on increasing your damage instead. Someone who plays conservatively and hangs on to their triple/swift/xeno is going to be able to do the standard rotation consistently, they'll just put out less damage than someone who knows how to cut corners and spend every spare triple/swift/xeno at optimal rather than conservative times.
As much as I agree with you that Thunderhead is bad, I don't think it creates any danger of DoT clipping aside from the way it might mislead new players into thinking they should do that on purpose. There's basically no pressure to refresh your DoT early unless you're so completely out of movement options that even a high-level player would've made the spot decision to do so, and insofar as there are unavoidable gaps in DoT upkeep, those are, you know, unavoidable. If some otherwise-defensible sequence of Thunder refresh and Manafont activation and so on puts you in a situation where your Thunder falls off and then stays off for 3 or 4 seconds before being reapplied, that's just how the job works, no more your fault than a failure to cast more than one Flare Star per astral cycle is. It's like how the GNB Bow Shock or whatever it's called DoT doesn't actually have 100% uptime either.
I don't think Manafont drift is a serious issue either because, like the very occasional DoT elapse above, it's just a fact of life that's no one's fault and therefore no one's problem. Like, you can, at any time, do a "short fire line" in order to line your rotation up so that you can Manafont on cooldown—you just have to cast Despair early, and bam, your astral cycle has been truncated. Obviously, doing this means you lose out on one or more Fire IVs and a Flare Star, and therefore costs you more damage than being able to Manafont earlier would gain you, so you don't do it. But what's wrong with that? I think it'd actually be worse if it gave you better damage, rather than worse, to truncate your rotation to fit Manafont's cooldown exactly, because it'd be less mathematically obvious that it's a good idea and people wouldn't realize they were losing out on damage by performing the rotation the job appears to expect of them.Sure, it is true that if you close your eyes and ignore all the "damage shortfalls" then yes, you could consider DT BLM to be easier. But I don't like this jobs' difficulty to now come from managing an awful DOT system and manafont drift. I don't think that anyone who misses one F4 should be punished so harshly.
(On that note, I consider it poor design that casting Flare Star as soon it becomes available is a mistake since it doesn't refresh your AF timer. Yet another thing the developers appear to have forgotten).
That said, I agree with you that there should be a consolation prize for missing an F4 and that there's no reason for Flare Star itself to not refresh AF. I think I suggested somewhere in this thread or another that zeroing your MP with either Flare or Despair could automatically fill your Astral Gauge with dimmer/less valuable pips or something, and depending on how many actual F4s/non-zeroing-Flares you were able to cast, the final damage of Flare Star would be scaled somewhere between that of Despair's own damage and Flare Star's listed maximum potency.
Hell, they could just make Despair work exactly like Flare such that it gives you three pips when it lands (though this might make it look and feel weird to sometimes find yourself swapping to ice mode with 3/6 pips on your bar). The important thing to me is that a 6xF4 astral cycle should remain decisively optimal in terms of potency per second; skipping spells should be a best-of-two-bad-options thing rather than an obscure way to do better than standard.