I don't think the changes are meant to make new players previously intimidated flood into the job, precisely because the astral/umbral timers (which I like) are being kept and in fact being made more strict in some ways (messing up your astral phase such that you cast less than the absolute maximum possible F4s is now even more punishing than before).
I think the changes have three main goals: first, they streamline and make automatic things that were effectively already foregone conclusions/almost totally deterministic. This is why you just get a free thunder cast per phase for a predictable amount of damage: all the buffs to Sharpcast and the difference between the value of Firestarter and Thundercloud meant that you were already just throwing a free, instant Thunder every ~30s, which Sharpcast's recharge timer lined up with, and if you weren't doing that you were probably losing damage, so the actual utility of even having a separate Sharpcast button was highly marginal. It wasn't zero, but it might not have outweighed the hotbar space, weaving, and just straight-up button pressing it demanded.
Second, the changes make it some combination of rewarding and mandatory to actually use all your core spells. "Nonstandard" rotation wasn't used because it was weird or quirky or personally expressive; it was used because, by only casting strong spells and not weak spells, you could deal more damage per second. However, for what you might call the average or midcore BLM player (and what I would call myself; I'm good enough to do Savage raiding but I'm not at the absolute bleeding edge of the job), someone who likes the feel of the cast times and timers but doesn't want to install third party tools to keep perfect track of the server's mana tick and therefore know when or when not to make certain shortcuts and substitutions, it feels bad to know that casting Blizzard 4 or otherwise using your spells in an intuitive way is secretly only the second- or third-best thing you could be doing, and in fact that you're a chump for swapping to UI3 by casting B3 when you could instead be cobbling together something jankier out of Transpose, Lucid, and Paradox. So, they've firmed up the utility or the necessity of the spells that the very best players were skipping, so that no one actually wanted to skip those spells, because otherwise why are they there?
Third, freedom from the mana tick is a reward in and of itself, because especially if you itemized for spellspeed even an average player like me could find themselves depending on or getting screwed by the server's 3 second timer. I don't know all the nonstandard tricks but I do know to Transpose-Firestarter out of Umbral, and it's very common to wind up in a situation where that may or may not be a good idea purely based on when I'm getting my next lump sum of regen. As well, at the end of EW, it was entirely possible for me to be in leylines, do B3-B4-Paradox-F3, and discover that I only had 60% of my MP bar at the start of my next astral cycle. Awful!
There's some stuff I don't like about the DT changes - I want to cast Paradox in both my ice and fire phase, I want to use High Fire II for damage and not just for phase change, I want some kind of fun proc, time, or meter-based reward for using thunder spells that has a big up-front damage number - but I've been a BLM main since I started playing in ARR and I largely appreciate all the changes being made here. On top of everything else, I'm really looking forward to the button consolidation; as soon as I saw how various iterations of the PvP BLM worked, I was always annoyed that I couldn't have any of my pairs of PvE mirrored, phase-exclusive spells on a single, auto-swapping hotkey.