The Guildleve system was built specifically for casual players, and was not -originally- intended to be a system where you fail leves to optimize your SP gain. HOWEVER, this game does not have content for hardcore players, and thus, the guildleve system is the method of choice for grinding ranks. The reason the ability to abandon a leve was added was to cater to these hardcore players.

Once the actual core of the game is fixed, content becomes added, and more options become available, this will obviously become less of a problem.

Now, as it stands, apart from reward/sp balancing, there is NOTHING wrong with the Guildleve system. So instead of grinding on an already over-burdened development team to overhaul/change yet ANOTHER system in the game, how about you just wait until planned fixes are in place which will inevitably fix this issue without requiring the use of any development time on an already struggling game.