welcome Maldrak, hope you have a wonderful time here
not sure what you mean by grouping - if you talk about guilds / alliances it makes sense to join one as soon as you are in the game, for two reasons:
1st you can learn a lot and fast from experienced players, cuz there indeed is a lot to learn if you want to become good
2nd you can get useful stuff from guildbosses as well as let your dragons collect useful stuff when your guild has learned the skills.
well, whats your definition of endgame fun of course mainly depends what you expect from a game and the way you want to play it.
since you skipped the lvl 60 potion i assume you do have other goals than becoming an op player fast - in that case there is good news here indeed.
the game has so many aspects, so many possibilities what / how you can play, so if you want to learn most or even all of them this game will keep you busy for years, and thats a promise
the good thing is, you don´t have any pressure. it makes no difference if you max out fast or in some years, you can always decide to chill out, do housing, learn the many opportunities the dragons give you, doing fun things like midas games and so on.
for me every day in dp is unique - i always do whats most fun for the moment, no need to stay always in same dungeons and farm same stuff