Unreal engine v2 maps can be plenty big. Just look at UT2004 onslaught maps. They may not be as big as Tribes 1 & 2 maps can be, but that is not what is really wrong with this game
Although some may argue the size of maps doesnt matter, in Tribes it DID matter to a lot of players. Its one example of how the makers of the game underestimated certain elements of the game that players loved, especially with T2 where larger games would be played with 40+ players using vehicles and such. The whole sense of free movement within the environement of Tribes is one of its trademark characteristics.
In regards to Unreal. The older engine used in TV is horrid. I'm sorry but it not the best for networked games especially with a lot of players on a server. Granted the TV engine is tweaked, but even Unreal 2 was pretty bad. TV did not use the engine for Unreal Tourney 2004. Perhaps Unreal 3 will be vastly better in terms of its network performance VS the eye candy we see.