I think buying a weapon it should start off AS good as the previous weapon and not force you to upgrade it max to make it have a difference of only 200 bullets.
I wish you could speed up training a little bit more, gets kinda bothersome leveling up new monsters, it takes like 10 minutes. Otherwise awesome game.
When you get farther into the game, even just to rank 7 in the first coliseum, it gets a little grindy. You need around 600 for a new team member, which is reasonable, but you need a set of gear for them to help out. You only get around 100 gold every uncompleted battle. Also getting levels could be made a little easier too. Hope you can make some changes soon. :)