Basically yeah.
A-RPGs by their very nature are optimization games. That is the gameplay.
It is never about what others do (as some people here seem to pretend) is it about what you as an individual player do. And the choice between solo vs. 4 player (or as I also repeatedly call out, 2 or 3 player vs. 4 player) are not balanced choices for that individual player.
One of the issues currently is that group play is easier than solo play, so solo players should get a setting that would make the game easier for them, while getting more rewards?
Meh, imo the game should become harder, not easier. Fix the difficulty issues in group player first instead.
It IS a solo player game.
Just not a very well balanced one (and arguably not a very fun one either).
Where exactly do you believe there is a contradiction? 
Most A-RPGs have multiplayer, yes.
Just like most A-RPGs have singleplayer.
What reason do you think that is?
It ought to be so simple.