My further research into exploits led me to this conclusion: in fact, the game can be played without long rests. How? It turned out that the bug with "infinite restoration" of slots is wider than I thought. It concerns not only Gale and not only magicians. It applies to any slots for any characters in general. At first I thought that only Gale restores slots, and other mage characters do not. Then I found out that this is not so. Yes, if you spend magic slots on any other character, and then immediately send him to “change class” with the same class, the slots will not be restored. But if you change the mage class to a class where there are no magic slots, and then change the class again, but to a mage, then all the slots will be restored. However, this is only part of the problem. Another problem concerns Bards. Their ability to provide the team with a short rest is also restored after the described procedure. Given the above, theoretically it turns out that the team may not take a long rest at all (except in the interests of the plot). One of the consequences of this problem may be that you can save on potions (drink once and go out for as long as you need). Another consequence is unjustified combinations like this: before the battle, your mage gives buffs (that do not require concentration) to another character, and then this mage goes to the camp, changes class to warrior and joins the battle as a warrior.
I strongly recommend that the game creators rework this aspect. I hope that in the “Golden Edition” we will see different game mechanics in this matter. My suggestion is this:
1. Make a limit on the cost of theft for each specific merchant (as in Original Sin 2). It's strange that this mechanic wasn't included in BG3.
2. Limit the possibility of changing class (as you wish, but it is possible - through a progressive increase in the cost of each class change cycle).
3. Fix problems with restoring slots after changing classes.
If these changes are not introduced, the balance of the game will seriously suffer. For example, there is almost no point in accumulating food for a long vacation. Moreover, there is no point in hoarding any goods at all. Why, if you can just endlessly steal from a child who won’t even call the guards?
