I give some level 5 spellcaster stats in the spider lair thread if interested. You'll see just how powerful a mage can be at level 5 with just the Dragon's Breath spell. I didn't even have her use lightning bolt or fireball. 😁
The higher the levels, the tougher they get. If you don't limit long rests, they become OP.
Prepare to be disappointed because so far all signs indicate that Larian is not going to do this.
If you look at all of the most popular D&D games, none of them had limited rest, and for no reason.
The game is clearly not designed for limited rest along with the fast travel system, camp, talks or even the balance of fights.
It is unlikely that they would suddenly change direction by 180 degrees.
Players do not like to manage resources in rpg games for a long time and if it were not for the fact that the presence of rest is the core mechanic of D&D, it would most likely be removed.
The fact that the game will not be balanced, really hardly anyone cares as long as the game is fun and there will be no situation when the character will be useless.
The D&D balance actually died when they decided to make the AAA game.