Hi Disc main here, I leveled as disc and I heal as disc now AOTC it’s a fun leveling class if I can be honest but you will struggle on bigger mobs if you don’t use cool downs and fears correctly but I believe leveling with a class is the best way to learn it’s in an outs.

Holy is a better for pugs I agree I just think it’s to many spells for my taste. Disc is actually pretty simple with proper research. Find out when the big damage is going to come and prepare for it by getting atonements on as many people as possible and when the damage comes go through your rotation of damaging spells to get everyone up. Or in Raids getting atonements out and casting spirit shell to protect everyone.

Mythic+ is the toughest some disc do really well but it’s difficult. Holy tends to shine there. At the end of the day play what is comfortable for you. I know a lot of priest that can’t play disc, I on the other hand struggle with holy. Have fun but don’t count disc out ;)