Since you are concerned about balance, I'll assume this is for a game setting, and not a movie/book/etc. How to solve this best will depend a bit on what kind of game you are working with.
If this is for something like an RTS or CCG where pre-packaged skill sets are must, then sure, classing out casters like this makes a lot of since, but since they are pre-packaged you are also deciding what spell sets each unit has. It will be the spells you assign them that determine how the system ballences, and how they focus thier mana will just be a thing to add an extra layer of strategy on how to deploy them.
For any system where each character is created on an ad hoc basis such as RPGs. I'd say the idea of classing out your mages like this is going to make your system much less interesting, not more so. People's abilities are on spectra. You can be a little specialized, very specialized, a poor generalist, or a master of many things; so, the idea of taking base stats like this and jamming them into forced classes is not all that great for someone interested in creating a character. Instead I would give casters skill points to distribute between these 3 qualities so that players can better explore the meta that best fits them. 846
Again though, it will be the SPELLS you put into the game that make the balance. If you notice that recharge min-maxed players are dominating PvP add some new spells to help the other 2 classes out, or nerf the one spell that is being abused. Game designers often spend years giving and taking powers until they find a balance that is mostly fair, but in the end, it does not matter what you do, someone will always find something to exploit that people will find unfair, and there is a certain degree of this that you should just accept. When people start complaining about all three min-maxes having an unfair advantage, you know you've got it right.
If this is not a game, but for a story, I'd say ditch the idea of mechanically balancing it. It does not need to be balanced. If max reservists walks up and every one is like, "shit, it's one of these guys!" that is not a bad thing. Also, in a story, you have a lot of control over the perception of balance through your own narration. If you create scenes where one class wins a lot, the audience will accept that as the best meta, if you want balance, just narrate scenes where each class finds creative ways to gain the upper hand and people will believe it is fair and balanced. 846