I can agree to this. I understand the design decision behind a simple tank rotation; the main game of a tank is not the combos we use but the macro meta of the fight itself. However, combos are a part of this, and pressing globals is the cornerstone of this game. I don't necessarily think we need a dps-level of complexity, but I can understand wanting more. GNB and PLD both flow pretty well but have a lot of rigidity to them. WAR and DRK have periods of high action where you feel busy but the low intensity periods wear on you. How exactly to address this I don't know. Part of the issue comes from the (relatively) simpler encounters present at end game right now. After seeing that TEA has in store for players, I'm hopeful for more challenging macro-level stuff for tanks to do in upcoming content, but it's always a good idea to talk about how baseline rotational stuff can be improved.
I can understand the perspective regarding healers, and again I'm hopeful - having seen the sheer amount of GCD healing needed to beat TEA - that future fights will emphasize more of the "healer" side of a healers kit instead of the dps. As someone who casually plays a healer (WHM and AST) I find AST to be more functionally busy but WHM to feel more powerful overall. I enjoy the longer-term macro planning you get with AST, and I wouldn't mind shades of that being imported to WHM, as well as a bit more depth to healer rotation.[*]Equally valuable contributions to the party should come from roughly equal requirements of skillful play.
This is of course a variation on "effort/complexity should be duly rewarded" which is itself controversial and is likely a minority opinion by a slight margin if ever applied as broadly as to general balance or long-term metrics like rDPS. Still, many have argued as an extension of such that the skillful play required for healers to minimize their healing is still not enough to bring them up to the average skill requirements given how barebones their offensive gameplay itself has become -- effectively, that healers are getting too much output potential for too little effort or complexity. There has not yet been any thorough counter-argument save those already applied to the more general warrant. Others have pressed that the efforts spent in allowing for healer offensive uptime is valuable, but none have gone so far as to argue (except perhaps implicitly) that it is therefore sufficient.
But that's a discussion for elsewhere.
As far as it pertains to tanks, again I think it's important to gauge the contribution not just by GCD and ability complexity, but by the macro-level fight-centric stuff expected of a tank. I'm confident SE has more in store for us later on in the xpac, but I'm not against the idea of higher complexity in tank combos. Naturally I would want this to lead to higher reward (most probably damage, but it would be nice if some kind of mitigation and/or other utility factored in as well). I've been going through the thread Kabooa made, but I have nothing substantive to add as of yet. I'm a bit too focused in on the current state of the game, so all of my suggestions are - to use your words - adding another spinning plate to maintain.