It is intentionally convenient for the nobles of the Alzer Republic. That convenience also plays a significant part in Noelle's backstory.
Not really. I generally turn my brain off when reading these kinds of stories unless it's egregious. Also, knowing Leon's personality and how he does things, my reaction was less "this is stupid" and more "what kind of insane plan is Leon going to cook up with this time to stomp on everyone?" One thing you should generally recognize is that when Leon is quiet angry, it means he's in the process of hatching a plan to pay them back 100 fold.
For me, the most frustrating part of this manga/story is Leon's lack of awareness of how the girls around him feel, followed by how he's actually a complete pushover for anyone he cares about (this includes Marie, regardless of how he appears to treat her).