People do waste lily heals, though? If you're in an alliance raid, and you go a while without anything interesting happening, it's completely reasonable to burn a lily for no reason just to have Misery up for the next buff window.
WHM is mostly well designed at high levels in general. It is also the one class that has a gcd refund setup, but what I want for a more complicated dps setup isn't all refunds. What I want is reliable incentives to be using most of the healer kit, even if you're in content that has been massively power crept. It's not inherently bad for Void Ark as an example to have a lot of sleepy moments where you just exist.
Imagine, if you will, that spending an Aetherflow on a healing action ensured your next Biolysis would have double potency. This on its own would change the damage calculation of sch so that you _want_ to use an effective Aetherflow heal or mitigation, while leaving Energy Drain as a way to dump Aetherflow to avoid overcapping.
Or if breaking a Divine Benison then gives a doubled Dia.
I don't know sage or ast's kits well enough to have a good idea on what healing tools with charges would be fun to tie in to damage output, but what I think would be enjoyable is that if you are regularly rewarded for using most of your hotbar efficiently, even in casual content. Most of the healer players angry about the lack of damage rotation and the simplicity of healing don't do high end regardless.
I do not want more healing tools put in the category of "it's a dps gain to use this on cooldown". I think those are not very exciting, on the whole. "This is used on cooldown" doesn't involve that much more thought than "I lost multiple uses of this skill because there was honestly no point to doing it". There will always be a bunch of head empty roulette content. I would rather have the healing and damage parts of the kits more integrated so that I'm not spending eons with a full Fey Union gauge because it's not worth the effort to burn it.
IMO most healers want something to problem solve more than they want to press buttons that aren't your two primary attacks more often. Incentives to use your resources and not overcap them, while giving you flexibility in when you actually spend them, seem a pretty obvious direction to go in that's a lot more interesting than a 1 2 3 combo.