Modifiers aren’t additive and that’s why your numbers don’t translate to in game.
If they’re multiplicative, that only makes Mind Flay even better.
1 * 1.15 * 1.1 * 1.06 = 1.34
1 + 0.15 + 0.1 + 0.06 = 1.31
I did mindflay in game and it’s coming out to 2.86 with a full 5 stack of weaving so clearly something is off with your math.
Mindflay
(129x3)/135= 2.86
Holy Fire
374 (initial damage) + 100 (dot)/170= 2.79 Non crit
Not sure how else to explain it to you. You claim mindflay destroys holy fire and it simply doesn’t. Crit would ABSOLUTELY account for more then .07 (also that .07 is lower at the weaving level you stated)
And disc is absolutely more mana efficient. The only true argument is shadow is more effective at wanding with shadow dps wands. The damage on SWP is negligible (6-7 more damage or 36 total damage over the duration of the dot is a less then half my wand damage).
With that said I wish I had tried shadow with a shadow wand sooner. It’s absolutely bonkers.
Dungeons are pretty easy, to be fair. Not sure its as gloomy as you advertise.
Ive tanked with far worse just fine, but I mit.
It looks like parenting or teaching: deeps are all the kids, and you hope your partner/coworker knows their way around and draws aggro from you.
Dungeons are easy if you go slow and the tank always keeps aggro. If the group goes fast, or with heavy AoE, there will be a lot of group wide damage and you need prayer of healing to counter that. There are reasons why many groups explicitly ask for a priest healer, and the prayer of healing is one of them.
That is refreshing to hear about the aggro part (I agree! We can hold aggro) 
Im on Faerlina running alts of people who are already 60 and it flies. Overall, deeps know their limits and priests can usually go afk: whether I’m keeping aggro or not.
I actually love it when I have newish people aboard, and then it feels like vanilla again with slow, steady and more team play it seems 
I have been leveling a Priest and I am level 49 with my mount and another 190g in the bags. Stop by ALL the spells and pick up Skinning/Tailoring to make bake revenue.
I said it’s more DPM. That’s objectively true, and proven with math.
It objectively isn’t, as I have a proven.