Shrink the maps and turn DG into Dota-Arena.
I've been an avid Dota player for years and cannot deny that DG feels a lot like Dota. There are subtle differences, but for the most part they are very similiar.
In my opinion the biggest difference is that DG occasionally feels like an actual "War." This tends to happen mid to late game on smaller maps with more players than the map is supposed to support. For example 5v5 on Prison. Mid-game there are dozens of creeps all over the map and with 10 players, it is total chaos. This kind of anarchy almost never occurs in Dota (if it ever occurs in Dota, it is minutes before a match ends when the other team has infiltrated the base).
If DG embraced this "War" gameplay more often, it could offer something that is missing from Dota. Right now, most people will tell you the key difference between Dota and DG is that the heroes in DG are more complex. However, I don't think this is really accurate. The DG skill-tree isn't THAT complex and the multitude of items in Dota more than make up for the lack of a skill tree.
Shrinking the maps is probably the easiest way to ensure every DG match will feel like a War. You could increase the creep spawn rate, but that may have more unintended consequences that shrinking the map. It also wouldn't cut the travel time for heroes. One of the reasons Prison is so fun is it doesn't take 30 seconds just to walk out into the main arena.
MOR WAR PLZ.