That's also what I mean by complexity, in that we aren't made to use our mobility as much for DPS, just mechanics. So far dancer has the most "complex" part of mobility in that they have to worry about being close for aoe procs and buffs. Personally, I'd really love it we were forced to use our mobility for damage. Then we'd have to make sacrifices too, just like melees, if a fight doesn't go our way. Another thing to point out is, part of the complexity comes from optimization. Jobs in general are quite simple if we plan to just press buttons, but doing really well and squeezing the smallest potency gains is really where the complexity comes into play (for example, aligning rotation with buffs). I can't say for certain this expansion, but I know in SB, RDM is of course easy to pickup and play just like dancer. But one of the harder jobs to optimize because of the RNG and needing to make quick decisions to get the most potency you can.
As for Shiva, it would definitely have made a difference if the groups had 2 melees or 1 melee, especially in earlier weeks. Nowadays you can have 100% uptime in light rampant but executing that is still harder than being a ranged getting to be in lala land.
One thing to consider is that the entire point is to not incentivize single melee comps. It imbalances raids. We need to be doing low damage so that people don't take more than one physical ranged. SE is still most likely going to nerf SMN more so that double caster comps won't also be as strong as double melee comps. It's clear with their raid design that SE has been trying to say "If you're good, you can clear with any comp, but if you want the best, you go with this." The same way they allow dupes but still penalize your LB generation. More or less, 2 DPS spots are for melee only and the other 2 are for caster and ranged. Once SMN gets tuned, and melees being buffed a tad to compete with SAM, I suspect that will naturally be the case.
It's working for raiders who like this iteration over the prior (the top end whom this expansion favors). As someone that has raided as Astro since HW release and only now picked up dancer because it exists, I think the current system is far better than the previous system. It's not perfect. Sleeve draw is an issue and there's more that can be done with seals and divination, but I can wait till next expansion. One might think they'd revert the changes but I wouldn't count on it. Unlike say BRD/MCH, this card rework was part of an overall larger homogenization plan to remove glaring balance issues and undoing AST cards would mean needing to undo the entire design principle of ShB which is unprecedented, to say the least.
As for play rate, AST has generally been the least played healer with exceptions of Creator and Alphascape. Though that could be attributed to end of tier people going for their parses. Now with rDPS, there's no need for AST so you could just see WHMs not moonlighting AST because their DPS wants a padded parse. So really, people will play what they want. Goal should never be to make all healers have similar play rates. That's what lead to creator and AST being busted.