A lot would argue that classic is more casual friendly mostly because you don't have to worry about falling behind because you're missing your dailies.
Also because it's a much much bigger game, way more quests, more items, more dungeons, etc. The amount of solo/5man content is much higher than retail which means the casual player has a lot more to do.
I mean, for the last few expansions it's basically worked like: Level to max, spam LFD to get GS to raid, raid if your interested, spam LFR, done for the patch. Compare that to Classic where the 1-60 journey is a whole game in and of itself and when it's done you still have more stuff to do than you did in total in the last couple of expansions, then you have weeks of dungeons/questing/etc to get the gear up if you wanna raid and if you don't there's still casual content like upgraded dungeon sets.
Fun times ahead