The variety of game modes is achieved through the availability (and the possibility of creating) different maps and templates.
And here's some more heresy - why is the maximum number of heroes on a map limited to 8? Where did this number even come from? I think this number should be set in the map/template settings. There would be interesting game modes, for example, with a maximum of three heroes on an M-map, or 16 on an XL+U map.