Mages are weak early levels because they have powers later on. If mages are powerful early game and chucks magic all day easily then later on you will have HUGE balancing problems. Mages have AOE spells, these do not miss. Enemy has to make a saving throw, such as dexterity saving throw to take half damage. If they are able to chuck spells early, they will chuck spells even more later, why would you even play a martial class then ?

Martial classes are for consistent damage throughout the game and combat, mages for explosive power later on. I dont play 5e but this is what I know from researching. For me this is interesting because it has a trade off, I also play pathfinder kingmaker which also has limited spells slot. These slots start to not matter as much because you will have so many available spells and so many spells slots that your mage becomes super good. You just can't see it now because level 4 mage is not that powerful especially if you cast mage armor and stuff. Just learn to move your mage out of line of sight, it is super easy since you can move then attack or attack then move or move attack move. This applies to your ranged characters as well, you dont Have to play it like pen and paper. Learn to use terrain, or make the mage be behind your team so a high initiative enemy wont Instant sleep or kill gale. This is not much different from DOS 2 at all. Your squishies will die in tactician if you just straight up walk in because enemy has insane initiatives.

Regarding people not liking "RNG rolls", I absolutely disagree. A lot of turn based games have chance to hit, such as Pillars of Eternity, pathfinder kingmaker, Xcom series, wasteland 3, if I remember correctly battle tech but I hate the game, and probably more. It makes the game interesting. DOS2 is also a great game too but making this game more like DOS 2 will be crap because combat does not make sense with DnD mechanics. Devs either has to make a BG3 or DOS 3 it cant be in between.

I personally want to see a game with DnD rules and amazing graphics. Solasta has good gameplay but I hate how it looks and moves.

And to me it seems that you either want an easier game which is fair or DOS 3. But I would suggest looking into DnD games on youtube, it is an interesting game I think. And maybe learning more about will change your mind.