Two other thoughts:
Firstly, what Hexofen does do well is give a higher piece density than Glinsky's, let alone McCooey's, but that could be seen more as a case for McCooey's going 3-player - which Hexofen cetainly can't do. The three-way En Prise shouldn't be much of a problem due to the pinning.
Secondly, while rotational symmetry is the only option on a three-player hex variant, it is not quite as clear-cut with even numbers of players. A 4-player square-cell variant can have 180° rotational symmetry, but mirror symmetry between neighbours rather than full 90° rotational symmetry, so that armies alternate between King on te left and Queen on the left. A 2-player variant's symmetry can be worth reconsidering but it's not a one-way street. Hex Shogi, for example, replaces standard Shogi's rotational symmetry with mirror symmetry.