As someone who working on comic/manga/manhwa/manhua all the series all above industry. I don't get it why people decided it wasnt a good conclusion, your opinion is clouded by your judgement because your fav girl didn't win the war.
- Negi is in time crunch, he has family and had to ended the series in timely manner, he promised vol 14 will be the last. His manager and publisher already make the contract to those specify volume. Deal already done.
- You'd think this all the work from Negi? No my dude, the editor is also behind all of this. They try to cramp the storyline to fit and close the ending in best way possible.
- How and why this series even considered a downfall? Just because it was slow at first time, you can't do that in LAST VOLUME.
- He didn't need to address or even write finish the arc or giving closure to other sister, but he did. In his weird way, Negi did that.
Also, as an Editor, i work closely writer/mangaka, your opinion didn't really matter to them. This is their story, you didn't have a single reason to expect them to listen to your whine.