Yeah, I'm sure having you start in a Mazda Demio and forcing you to complete a series of gruelling single-corner timed challenges just to access better paying events would go down spectacularly well with the Forza community.
Ah, I'm not saying FM23's progression is well thought out per se, but most of the complains I've read boil down to "why doesn't the game let me do what I want from the get go?".
Any progression system based on extrinsic motivators (i.e. locking content behind levels, credits or what have you) on a sandbox title like Forza is doomed to failure, simply because it runs counter to the ethos of the game. And intrinsic motivators are a hit and a miss - had they put in a career system where, say, you start from driving slower cars and move upwards to big boy racers, which you could have bypassed entirely as you can bypass entirely the Builders Cup now, people would've complained about the career being "useless".
Again, it all boils down to people yearning for game mechanics that got old almost twenty years ago; not because they were bad, but simply because there's only so many times you can have fun playing a GT4-like progression.
I'll eat my words if a competing title comes out with a progression system that makes most people happy. But I don't think that's very likely to happen anytime soon.
I'm sorry but I don't agree with there not being a progression system that people could have been happy with.
Let me just propose a simple yet thought out plan. The short version. And let's use what we already have just to make it easy.
We have classes of cars, starting with E Class.
I'm going to give you 3 E Class cars to pick from to start your Forza Builders Cup career.
You choose car. Lets say you have 3 - 4 race Championships to do in the car. First one being beginner, second one AI PI levels rise and the third one PI levels rise even more as you see them starting to fit parts on their cars. The point being, in order to be competitive, you either need to:
A) build and tune your car or
B) possibly if you have enough money, buy a better car and take your chances.
Now all the while, maybe C, B, A cars are locked from competition in career (you can still use them in free play, don't worry).
Now upon completion, you can either use you tuned E car, which is now probably a D or maybe even a C car, and take your chances on the next series of events.
This chain of events can progress all the way through the Letters of road cars until we get to race cars after A Class and then maybe split off the beginner race cars into user selectable Beginner Race Championships. Mazda M-5 Cup. Mazda Formula Mazda. Maybe Touring Cars next. Maybe branch off to Vintage Race Car classes. Whatever.
This is my personal idea of a "Builders Cup". Maybe others don't like it it but that's what I consider a nostalgic career and ACCCTUALLY building. Lock higher end series until you finish lower ones. People say that in this day and age they don't want that anymore. I say BS. That's exactly what I wanted. I wanted to make only a certain amount of credits to either build my car, or buy a better one. Not free lance the game all over the place with nothing making sense and no feeling of completion.
Grain of salt and 2 cents.