I agree with so much of this. I think there is one thing too that you could have spoken about a bit more, but isn't something you might notice. The trinket and set bonuses definitely need to change. Neither are fun or interesting or really change gameplay too much. Especially for normal/heroic raiders like me.

trinket from a normal/heroic raider's perspective

I don't use the Sanctuary chakra. Why would I? Serenity is almost always the better option because the damage output of aoe is bursty, which the blue chakra isn't great at dealing with. I use it for Kromag and the last phase of blast furnace where there is consistent aoe, but otherwise only rarely when necessary.

Serenity is the all around better spell. It is versatile with a lot of uses, and the cooldown is short enough that I can make the most out of all of them. I can use it as a last minute save on someone's life if GS is down. I can use it to burst heal the tanks or a specific player before a big mechanic. I can use it on the move, it synergizes with a ton of other spells in the toolkit, etc.

So why would I use a trinket that requires me to stay in blue chakra for so long. Why would this interest me at all?

The trinket is the only thing that really "changes" the rotation or makes it more interesting/a different playstyle. The set bonuses don't, and if I'm not going to use the trinket then there is nothing. The current set bonus made a huge difference in my playstyle. DI suddenly became very good, it made me more mobile and it changed up how I played. The new set bonuses are just a passive haste bonus or multistrike of PoM. This isn't really interesting at all to me.

*Utility

I'm fine with the jack of all trades style holy priest, even with doing less healing than others. I play holy because to me it is more 'fleshed out' than disc priest, it feels like a fully spec. But I think we should have more utility to make up for it. For example, Body and Soul is one of my fav talents because it gives an on-demand speed boost to anyone that helps deal with mechanics. Unfortunately, I can't use this talent if a disc priest is in the raid.

And the feather is all around worse because of world lag and positioning. I need to click on it, place it and hope that the player runs through it and gets it, rather than it not triggering because of lag. I'd suggest making angelic feather work more like B&S by allowing you to directly buff a player, rather than place it on the ground.