They already know the solution to this. At least, I'd think they do. People need to be given an incentive to party for exp as a group vs. solo activity. That incentive ought to be faster exp rates. With thinking like that I don't think questing exp and grinding for it are mutually exclusive as far as taking place in the game. In fact, there should be greater exp rewards for questing as a group (and not just pissy pointless bonuses). SE just needs to figure out how to balance it.

I like group grinding. Not necessarily for the exp, but because I find that it's far more interesting than running about soloing "kill x number of this mob" quests repeatedly for exp. You meet interesting people and the community comes together. It's a fun way of doing things to me.

So both forms of leveling should exist, but if SE creates the game such that grouping for exp is a chore then people will naturally gravitate to just do their own thing; something which made 1.0 kind of stale. What we don't need is XI's forced grouping. You weren't getting any exp unless you were partying in XI (short of BST and SMN perhaps). That kind of strictness is outdated.