As someone who's done every healer, and swaps for savage tiers. I'd say Sage is the "easiest" because the toolkit is almost perfect out of the box and doesn't require additional steps like placement, which adds to the simplicity. You have to place Sacred Soil but you don't for Sage, it's based on where you are it applies, and so the likelihood someone won't get mitigation is much less. Granted if you sit on stacks and don't use them properly, it's going to feel more work because you aren't using the resources it provides over time. A real 'just press buttons' job.

Like there isn't a single change Sage needs, doesn't struggle anywhere. If anything the game needs to keep up with Sage. Pneuma is revolutionary in that it's a huge HoT tick and not a straight heal, so the game can take a few seconds longer to update the party list UI because it's a tick.