I think there is some concern that scaling enemies would make going up levels FEEL kind of meaningless. A lot of people would feel they're never really getting any stronger, since they're always on exactly par with the enemies.
I do agree about the lack of freedom, but without looking at the whole game at this point its impossible to tell if it opens up or stays 'railroady' the entire time. We're only seeing like 20% of the content at the moment.
Maybe the problem really is just trying to balance everything so tightly around 'levels'. I'm not a game designer, so its hard to imagine any design that might be 'better' without resorting to something like 'MMO areas' where everything is a flattened difficulty.
