If you’re suggesting that you want to make a game based around magic and level progression, you simply haven’t given us enough core details about the rest of the player experience. People aren’t able to fully determine if your idea is good or not - because you haven’t actually explained anything else that goes on.
All I am aware of is that magic is involved with some form, and that you’re going to have level progression, milestones and different abilities. The three main points you have made sound good, and together it seems like a good idea, but I simply wouldn’t play because I’m not intrigued by the lack of detail you’ve provided. I also understand that you want FFA but I don’t know how that’s going to be implemented, and its something that could better or worsen my experiences as a player.
It sounds like a solid foundation to start off with, but you haven’t provided any input on creative or artistic direction that would probably impact a lot of people in their decision making regarding your main question. I’m sorry if this sounds like a rant, but considering this is Game Design support, having as much information about your game idea will probably benefit you and allow you to get more feedback.