Every planet has quests that require a team. If you can solo all of the H4 content without out-leveling it, then you are in the extreme minority.
Yes you are correct. Each planet has roughly 1 or 2 truely group-oriented Heroics. They are also purely optional, and most can be done in less than 30 minutes each.
It's an MMO. Group content should be the majority of content, not a few optional quests. Designing an MMO to be 95% solo game makes no sense at all. It would seem to be pretty obvious to me that making a multiplayer game actually mutiiplayer for the majority of the play experience would be a no-brainer.