The boost does worry me a little. I'm a returning player, and I did it on a DK (something I'm familiar with from Cata days). I tried a few others, but man felt off. I just wish I leveled through the Bfa content rather than through AV. Granted, I was able to get 120 super fast, but I don't think its for the casual/new player or someone picking a new class.
Boosts are better for ppl looking at a new server and maybe want to save on leveling all the way through - but it should be a class already familiar with imo.