So, first let me get this out of the way, i wont be playtesting the system, because reasons. Paizo has produced a lot of products i've liked over the years, starting with 3.5 era dragon, so i do still follow this playtesting project.
The specific problem with the playtest materials will be discussed later (the nature of the classes)
So to to get this out of the way: Very few people like playing healers, at all. Fundamentally it is because it is a reactive playstyle, you blow per day resources, often out of combat (because healing has historically not been effective in combat, or at all, more on that later) meaning you usually have to save resources that could be used having fun at the table, and in the cases healing is effective, it is still reactive and rather boring, unless it comes with interesting rider effects. I played a cleric once when i was new to roleplaying in 3,5, hated every second of it, then we discovered how effective wands were, and i had fun again.
The second issue is the old "sacred cow" in DnD that good healing has to come from a divine source (and druids count as divine). Most of the players in most of the groups I've played with have been atheists, and a lot refuse to play divine characters at all (As a christian myself, you could say their religion forbids it :P). This is not tied to any game mechanics, but it is an issue.
The most fun I, or anyone else in my main group has had with healers was in 4th edition dnd, where healing was effective, tied to surges, and came with interesting riders all used as bonus actions in combat.
We left 4th ed because of the gamist and boring skill system (the playtest is doing this too, please stop), and tracking the amount of rider effects and conditional bonuses got exhausting, but everyone agrees that was the most fun they had as a healer.
Suggestions: either go with the stamina/hp system used in starfinder, and make healing in combat interesting, or tie effective out of combat healing to the medicine skill. In d&d 5e, the most effective healing resource is interestingly enough the bandage feat.
The cleric class in the playtest is really, really good (probably top-tier) but people might not play it, mostly atheists but also people tied to abrahamic religions, because worshipping another god in game is too much for some people as well, it does not matter how good you make a specific class, people might still not want to play it, and it also prohibits class diversity and limits design space for new classes.
I was going to talk about wands of clw and the like as well, and how they are frustrating from a dm perspective, but were absolutely necessary in 3,5 and pathfinder, but that might be another thread.
