Controller space limits how many buttons you get.
They'd have to not give you a new healing toy sometime too.
I've been healing in mmorpgs for a very long time, all the way back to 2002. I played SCH in HW and absolutely hated it.
My favorite iteration of healers was actually classic vanilla wow and TBC, where there was a lot if downtime and knowing when to heal and when to slip into the five second rule to regenerate mana was an acquired skill.
I don't like to have to push dps buttons, I'd rather be healing. I do the dos thing, because it's expected of me, but I don't have to like it.
So what if people dislike the added damage output and keeping people alive is harder? Not every role is going to be for everyone.
I could see maybe adding another dot, but dots are fire and forget and boring as hell. Combo skills are also boring. Maybe bring in something like wow hpal glimmer of light, where using an ability puts an effect on the target that heals or harms wall targets with it when you use abilities on other targets, or have dps spells reduce cds of other abilities so you can use your cds more often? Ability interplay can add complexity without going "hurr durr MOAR dps button pl0x" like I keep seeing suggested.
And maybe there shouldn't be so much downtime. Maybe you should want people topped off instead of sitting at 20%. Maybe damage varies more, same ability could hit harder or lighter randomly.
Anything other than "just add more dps buttons lol". There's plenty of other options