Hey buddy, I think you're forgetting that wow is part of a company and it's one of their major products they've been relying on for years. You may hate BFA and all the people who are still subscribed and playing BFA, but I can assure you Blizzard doesn't think that way. Imagine you sign up to go on a brand new cruise ship. The cruise ship company has a bunch of loyal customers who have been going on their cruises for years so they let them tour the new cruise ship the day before, however they decide to let new customers go on the tour for a small fee if they want to. That's what this is like. They're giving a little kick back to all the people who have stayed subbed to wow. I haven't played wow since the middle of legion and I can totally understand why blizzard would do that. You may think classic is all that matters. Blizzard still cares very much about the BFA players.
This Shadow Talent Build is the fastest for Leveling Up a Priest Class from 1-60 in WoW Classic patch 1.12. Spamming Shadow Damage DOTs while kite mobs will be the name of the game with this build, having the ability to sustain your health is just a bonus. You will just need to make sure you are stacking enough spirit so you don’t run out of mana often as that will slow down the levelling process drastically.
This is the lamest excuse to try and pin it on a cash grab. Tbh this is just you complaining to complain, there is no issue. If you wanted to play classic on launch you'd have to sub before hand anyways you're still paying month to month you don't pay by week. The only way you'd lose that money is if you quit before your sub ran out later on down the road.