SE, the 7.0 BLM changes will not increase engagement. They are completely-pointless.

[Galvuu]

Well, Fire IV has always been BLM's single hardest-hitting and spammable spell, so the goal (on single target, anyway) has always been to maximize the density of Fire IV (and Despair) of casts in the total list of spell casts populated over the course of a fight. Even if Flare Star didn't exist, you'd still be trying your hardest to execute an astral cycle consisting of six F4s, one Paradox, and one Despair every time you can, with an awareness of an imminent boss jump/death just leading you to cut your astral cycle short by casting your Despair early.

Various transpose/lucid/paradox tricks ultimately amounted to purging as many weaker-than-F4 spells from the rotation as possible, but if by some miracle you could still cast six F4s per astral cycle while also skipping B3, B4, F3, whatever, that's what you'd do, because it would further increase your F4 density. So it's just generally true that you always want more F4s, and lose out on damage if you can't do all your F4s. DT knows what the maximum number of F4s is and rewards you for hitting it, which is a bit of a win more mechanic, but doesn't really change your basic goals in so doing.

This is a simplified view of the overall problem, in fairness. The goal, in reality, at least for EW, is the following: "how can I maximize the average potency of my gcd?". This includes many aspects- maximizing your powerful spells like Despair, Paradox and Fire IV is one. But so is keeping Thunder rolling without overwriting it and using your instant casting ogcds (Swiftcast and Triple) on Despair as much as possible (since it's a slower cast and doing so grants you more potency per second).
In addition to these, another aspect of this is "how can I minimize the number of weak spells in my gcds?" and "how can I keep perfect uptime at all times?". And it's these last two that make DT BLM problematic. For the former, they're attempting to force you to use them. For the latter is where the "rigidity" aspect comes into play. It's just like the hypothetical I gave you exemplifies- if movement, or a mechanic, or downtime, or just an honest mistake forces you to lose one of your "builder gcds" (your Fire IV), then you lose a very powerful gcd (Flare Star) for the whole fight, with no way of recovering it. It's like losing a Xenoglossy for not casting 6xFire IV. This is the "builder>spender" pattern. People have given good examples and thoughts on this in other posts.
It's really thinking about the problem a bit differently (and more completely) than just "I wanna cast as many Fire IV/Despair as possible".

(Oh my God, I replied to the wrong post... I'm sorry. I'll leave it up because I think the info is still useful...)