You want to maximise "Fun" you configure the game for Axis-Only Comp-Stompers and/or 4v4 players, both of whom are groups of people the 1v1 Herrenvolk tell us must suck it because of the all-important competitive balance.
Again, balance is not necessarily causative of fun, therefore, the statements of 1v1 AND 4v4 fun are not mutually exclusive except in the particular, or accidental.
Additionally, players who tend to be more casual often have a lesser grasp of the game's mechanics often come up with wildly inaccurate claims as to the game's balance, refuse (or, more likely, simply not care to, as they admit they are casuals) to improve, and find relatively petty reasons to dislike certain aspects of the game. 4v4 players, compstompers, etc. tend to be casuals.
So, there is less practicality, or even magnanimity, in designing for them insofar as any design that must exist might throw the two game modes into conflict, for their perception of fun due to balance would be largely unchanged.