Probably close between ARPGs and MMORPGs?
I assume you mean they sit behind screen mindlessly repeating the same task. TBH if you break down any game is fundamentally a similar thing - MMO’s and possibly ARPG’s because of the clan and team aspect often create real world friendships, clan meet ups etc — thus you could argue that Solo Games are for the real life losers.
Hard to say, DotA 2 for sure has its fair share of no lifers
I don’t think that’s true for story-driven solo games. They usually require much less time investment and much less repetitive gameplay. That gives you more time for other efforts and endeavours – be it friends, family, non-game hobbies, or well other games.