shrug. All classes shoudl be made the same way? Why? Are all players the same, or something?
I don't see why we should not have some classes be complicated right out of the gate, and some classes just really simple, and some as you describe above.
That question is understandable let me explain. The reason for why this should be the case comes from the combination of 2 (and a half) design goals:
1. D&D does want to fulfill distinct class fantasies with a limited set of classes, since niche protection is important aka different classes should be different from each other in mechanics and flavour. In a game like League of Legends you can just create a new character bob, which does similar things like another character but is easier/or harder to play. In D&D introducing a hard to play warrior on top of the existing (easy to play) fighter will feel bad since they still kind of fill the same niche/ class fantasy. (Especislly since the fighter is vague already). So D&D is more sinilsr to magic the gathering with its different but still broad colours.
2. As a game you normally do not want to limit your own design space for the future. So if you make a class like the 5e wizard, where the base class already has a lot of power and complexity, you limit your possibilities for subclasses a lot, because there is not a lot of space. And combined with the class fantasy aspect mentioned in point 1, this also means that if you make a complex base class (or a tooo simple base class with a huge power budget) you no longer have the space/possibility to make a simple character (or a more complex) with the same class/power fantasy.
2.5 inclusion. You dont want to exclude people (children, old people who cant remember long texts good enough, people who might have some problems concentrating on overly long texts etc.) From playing certain kind of class fantasies. There is a reason its called "You are a wizard Harry" and not "Sorry only people who love reading long texts and learn them by heart like Hermione can be Wizards, Harry".
Here's is a question:
Must the simple arcane caster have spell slots?
Because to me, if we're talking about a simple class, then we're going by the idea of being as simple as the fighter champion in fifth edition. So a simple arcane, caster and a simple divine caster would be a class that does not have spell slots..
Why would we assume that something like "spell slots" are even a thing?
13th age does not have spell slots in its 2nd edition and is made by 2 former D&D lead designers.
But of course there is still some form of ressources and the question still stays if a simple class needs to have ressources.
I would say not necessarily, but having classes with no ressources and classes with ressources in the same game does make a fixed adventuring day necessarily.
So one could also do it like 13th age which has "arcs".
So in a 6E this could look something like: Per arc you have 2 short rests. Between 2 short rests you have 1 full fight or 2 half fight. (Making an adventueing day have like 3 full fights or up to 6 small ones).
This allows to make sure classes with no ressources like potential a simple caster are balanced with classes with ressources like potential a full complexity wizard.