We have both? Did I miss something? As far as I know there is no effective way to level as a group in FFXIV, because it is not implemented properly. I am not talking about doing guildleves with a group, but the traditional party like in FFXI.
What do you mean by "not implemented properly"? You can make a party, go to dungeons and kill stuff for SP. Mob grinding it is. I don't see what's stopping you.

In FFXI we don't have "both". We have quest grinding, and that's it. "Group based EXP grinding" is a shady concept and can apply to guildleves. Quest grinding and Mob grinding gets the point better across.