While I agree with almost everything you're saying, this point isn't completely true. It kinda hurts me to say this, as I started playing BLM in HW where being a steady damage dealer was its thing, every expansion moved BLM away from that and more into a burst job.
This is the damage profile of the BLM dps on 12Sp2 in EW, a dummy fight, overlayed with the overall raid dps:
You can see that, for the most part, the peaks follow that of the general trend. By EW, a lot of mastering BLM was tied to actually fitting your burst (3/4 Xenos, Paradox, Thundercloud and Despair) into the burst windows by manipulating your fire lines to get the required length and mobility.
DT might go back on this trend, but I feel the triple Polyglot stack and Flare Star somehow further pigeonhole BLM into this direction.
As an aside, and this is an idea I picked up from playing Picto, making Flare Star into a slower cast (like 5s) with very high potency (think something like 700 or 800
before the AF multiplier) might help with mobility. I can't begin to describe how
comfortable it is to be able to use Holy in White/Comet in Black and Swiftcast a motif to get 8s of mobility. I feel doing something similar with Flare Star, assuming they're committed to that horrid spell, is a good idea mid/long term.