i mean blue mage doesnt feel like that i think, as long as each gcd cd thingy has different cooldowns that dont line up perfectly it shouldnt be an issue. you can also prevent button bloat by making things do more than just 1 single thing. i quite like when buttons become other buttons situationally to combat button bloat but still keeping actions in the game.
its just pragmatics. even if i dont necessarily agree with said complaints i think its best to find a way to avoid them. i dont mind when more complex jobs are slightly worse than simple jobs, but theres usually a lot of complaining about balance when that happens. which eventually like you said leads to the current situation.
if theyre going to future proof that balance i think theyd have to give whm something, doesnt even need to be something too big imo. like maybe making using a lily heal reduce assize cd by X seconds in addition to charging the blood lily. whm would still play the same to pretty much everyone, but it would have a bit more going for it when optimizing, which in turn raises the ceiling without affecting the floor.
just to put into perspective how small the extra dps potential would be: the gap between highest dps and lowest dps healer is like 3-4%. if whm's extra *thing* raised its dps potential by even as little as 2%, it would actually be a huge deal for it to be competitive in speedkills and the like. and yet, the not-optimizers would not even care about such a tiny damage boost. this is what i think could be ideal, as that extra effort could deter a lot of the "why is babbys first healer better than mine!" complaints, while most of the "target audience" would probably not even notice it.
i guess theres also people that just like to get better at their own job, and wouldnt want to "graduate" from whm once they got too good. idk. like i said i think it would be best if whms nuance was subtle enough that most people wouldnt care about it, except for only those who really want to push whms limits. i see it as a win-win if executed right