The ladder mappool is indeed quite... conservative in this aspect. This is because of the mandatory nature of the mappool: you can force the other clan to play in a level if it's in the mappool. For this reason the original mappool was really small and very uncontroversial. The fact of the matter is that people pay a lot of attention to their map choice, which is why so few non mappool levels are played. The opposing team generally refuses. However, lately certain clans seem to be very good on one map but not as good on other maps: RL regularily hands everyone's asses to them on distopia, VS is very hard to beat on JE when Warrior plays. You can use this fact to play other levels if you want to. Just tell your opponents: do you want us to crush you on distopia or can we give elcas a go? (Yes, you should play elcas. It ownz.)

Contests tend to produce good levels, yes. Tournaments should definitely make use of such contests. If the ladder should is another question, but I'm not all that opposed to the idea myself


Edit:
For sbv2 see above. Zaitox wasn't suggested last time the mappool was expanded and therefore hasn't been discussed properly yet. The first time around we picked a very small uncontroverisal mappool on purpose