In the past, you've often taken individual actions I've proposed and asked the question of "what is the point?" Why eat up another spot on your hotbar that feels like padding? The thing is, there is a worthwhile argument to discussing what purpose different actions serve to a job's overall gameplay feel, and in truth, it's very difficult to identify that on paper without having a build to test it in. There's nothing wrong with asking that question, which is what I did for the 1-2-3 combo. And I would even ask the same thing of actual Machinist. I don't feel like a flat 1-2-3 combo with no sort of earning at the end, or branch to generate something different, is a good investment of hotbar real estate for a healer.
And like I said, I can see potential for how you could do something with a combo for Sage, even something as simple as a combo where one branch ends in healing your Kardia target while the other ends in granting a mitigation buff on them. It's like a reverse Warrior essentially. That's something that I honestly don't really care for, but I don't think is a bad idea either. The only criticism I'd say of the rest of your concept is it pretty much is just sparknotes Machinist. Taking inspiration from other jobs isn't a bad thing. I think it can be done effectively, but outright mimicking other jobs I don't think is the route to go on. That said, ideas have to start somewhere, and I could totally see someone joining a design meeting to discuss a Sage rework, perhaps, and saying "alright. What if we had healer Machinist? Here's what I started with..." And from there, the team takes that seed concept and fleshes it out to be its own thing.
The thing that I feel is most important about what I said, however, is that the 1-2-3 combo doesn't actually compliment this particular thread topic. If an ARR Scholar player could juggle their DoTs effectively, they'd achieve roughly 80% of the total possible damage they can do with their GCD and have roughly half their GCD casts remaining to spend on anything else: idling, moving, thinking, healing, and what you lose from missing casts of Ruin was considerably less than what you lose per cast doing that now. Cleric Stance made ARR healer DPS punishing, and asking the average player to manage 1 Dot with a 15 second duration, 2 DoTs with an 18 second duration, 1 with a 24 second duration, and 1 with a 30 second duration likely wouldn't result in perfect DoT uptime. But if you created a healer that had a variety of more forgiving DPS tools to work with now, things like charges, cooldowns, resource gauges, etc that the average player can far more reliably use the max of, and balancing potencies so that managing exclusively those cooldowns, resource spenders, procs, etc. results in roughly 80% of the possible damage you could deal, that would make healer DPS more forgiving than it is now.
Because now, every Glare/Broil/Dosis/Malefic that a player loses to healing, idling, moving, etc. counts twice as much against them as ARR Ruin did. If you want an environment where more casual healers don't have to worry about hitting enrage due to less efficient DPS uptime management, that would serve your goal better than the current healer model which puts more pressure on squeezing every last Glare/Broil/Dosis/Malefic out of your GCD than ever before.