I would take a bit farther and mention that a fly reel should also hold all of your intended line+backing as well. This is a definite consideration with the movement towards these bulkier weight forward and spey/switch oriented lines.

The balance thing, well that is less of a characteristic and more of a math problem/feel sorta thing i suppose and is solvable within any given line of reels regardless of quality.

Yes, the fly reel is a fairly simple beast of which very little is demanded or needed. That having been said, how boring would it be if the reels were designed as simply as their required functionality could dictate. That would be like only having one color of ascot.