You'll forgive me for not believing the claim that healer downtime gameplay, specifically dps options, must be simple, that 1111 is actually good or that "interactions are forbidden" or would provide a negative effect by healers trying to optimize after playing a WoW healer in something as simple as LFR, having plenty of constant and spiky damage all over the place while having more elaborate downtime gameplay for something that I was able to maybe 30% of my time tops.
The servers or healer brains won't suddenly explode if we have options, something to strive for as we get more and more practice while someone that still lacks this practice simply focusses on fulfilling their primary role. As I did in LFR after hopping into it for the first time in years.
Interaction between heal and dps spells would work, interaction between dps spells would work, rewarding optimized gameplay would work, having more options in general would work. How I know? Because FFXIV is so far the only game that actively refuses to give any of these - pretty much every other MMO I ever played, both old and more modern ones, weren't so stubborn about refusing to give options and it worked perfectly fine.
But somehow in the world of FFXIV that isn't possible, servers would explode, nobody would play healer, baby healer brains would explode and so on.

And I'm firmly against 123 combos for healers simply because they're indrecibly inefficient in terms of button economy while barely adding anything.
Avoiding button bloat is a constant issue and a 123 combo takes up 3 buttons for something that gives very little room for error since it's so binary, easily committed to muscle memory and doesn't involve any decision making. When we want to add engagement to downtime gameplay it's important to consider the cost (how many slots would it take up) vs reward (how much engagement and skill ceiling it provides).
And basic combos cost a lot for little reward.
Branching combos are another matter, however they are best for more than 3 buttons. 4 or even 5 is more realistic here to make it worthwhile.
Procs or cooldown/ dot duration decreases are also more efficient as they "scale" with your gameplay level and are great for adding synergy and interaction.
Something like a Mudra system or modifiers like Eukrasia or procs are good options as well and can be designed in a way that they "scale" with gameplay level as well.
Basic combos are barely a step above the skill ceiling being firmly pancaked against the skill floor as it is with 1111. You just hit the ceiling way too easily and then there's nothing more to it. If they decided to give every healer a 123 combo with 7.0, I'd laugh my ass off over how tone-deaf and off the mark it is. Healers are still the only role that gets the bubblewrap treatmen to this extend.