Inevitable Job Simplifications?

[Dahlinea]

Just answered your own question...

Having a basic spell set as baseline (Ruin II and Ruin III) and a lot of other GCDs and OGCDs means that the job was modular enough for you to actually move around pieces of abilities within the rotation to match the mechanics of the fights while trying to maximize the usage of your main basic hardcasted spell and preparing Further Ruin stacks and aligning oGCDs till Bahamut/Phoenix come from CD.

Now what's the baseline for new SMN? You have a forced Summon Bahamut to do to access your 3 legos, where 2/3 pretty much trivializes cast positioning since you can Swiftcast Slipstream. And talking about Slipstream, unless your tank loves to waltz around the battlefield during the fights, bosses' target circles are so big in this expansion that you'll rarely miss any of the ground AoE ticks. You have to also cast Ruin IV that's on a timer and it's also instacast, cast a Ruin III (if you didn't forgot to press your buttons for 2 seconds looking at the scenary) and proceed to Summon Phoenix to keep pressing the same button six times and Energy Drain (to hold Fester for Bahamut, but that's way too advanced isn't it?). From there you're forced to repeat. Sounds great, right? But all that is straightfoward and the game enforces this general path on you.
That's the baseline for new SMN which is also your near optimal rotation. That's why the graph shows a horizontal line indicating how the complexity of SMN pratically doesn't change from its entry level to its best performance, aside from meager tweaks along the rotation. Things that you had to think about and choose carefully during fights are now enforced in a general path with little to no meaningful choices, given the insta cast nature of most of current SMN spells that you HAVE to use regardless of what situation you're in.

The primal optmization is debatable but if you hold your bursts you'll be left casting only Ruin III, the thing you called braindead before.
There's nothing esoteric about spell speed. It always changed the APM of caster jobs that rely on cast/recast times, and that was true for old SMN too. The difference now is that new SMN basically doesn't have any casted spells so they moved the effect of spell speed recast times to Summon Bahamut/Phoenix and their spells. You just put the minimum amount of extra SS to be able to cast 6 of their spells, the rest going to Crit and Dhit, and just call it a day until/if the devs decide to change the modifiers of these stats in middle of the expansion, which will affect all jobs in such cases (if there was any case like that in past, I don't remember)

Also... Hello there! It's your favorite cultist again trying to make you see the light!