I think that's the sticking point (and maybe a bit of a sematic issue). If something is designed to perfectly meet its goals, but those goals are "broad acceptance and marketability", rather than "be the best X possible", does that mean its design is good?
Like you said above, you (and presumably all of us) can recognize features of the Porsche that obviously exceed that of the Ford F-150; it's why you used it in your example. If we're not complimenting the design of the Porsche in comparison to the F-150, what metric are we recognizing as being better?
That's the rub, isn't it? It goes down a subjective wormhole.
I think that for most people who are "really into cars," (car design, sports cars, etc.) they would agree that the Porsche 911 is a "better designed car" than the Ford F-150. In some abstract sense.
In the same way that people that are "really into movies" would say that, for example, Drive My Car was a better movie in 2021 than Shang-Chi.
But Drive My Car overperformed to $15 million at the box office worldwide.
Shang-Chi was #2 worldwide (COVID) with $432 million.
And I am quite sure that there are many people here, if not most, that would greatly prefer the "design" of Shang-Chi to Drive My Car.
I think that people often look down on things that are broadly popular and accepted, because they are broadly popular and accepted. But that requires its own type of skill. It's ... well, it's not easy to design something amazing and awesome, but when you are designing for a niche market, you also have fewer constraints- you are just designing something for that market, or, in the TTRPG market, you are designing something that doesn't have to worry about broad acceptance. Designing things that are broadly appealing isn't easy- because you have to design it so that lots of people like it, not just design it for a small number of people. That means that your design will always be a product of compromise, and trying to determine what boundaries to push, and what will remain palatable to a lot of people. That's not easy.
So that's why I default to being equivocal; the Porsche 911 manual may be, in some abstract sense, a "better" design- in the sense that it is better for those people that are really into cars, especially sports cars, that like manuals, and the feel of driving (as opposed to mere transportation or use for work) ... and also have the money for purchase and repair. But it's certainly not a better design for anyone outside of that niche. And there's a reason that Ford puts its resources toward the F-150, which is a better design for that use (lots of sales for a vehicle that people like).
It's the same with TTRPGs. WoTC could make some custom, indie-inspired bespoke game that is absolutely amazing and appeals to a small number of people. But why would they? Why would WoTC make the Porsche 911 Manual of TTRPGs?
Which is why I don't get the complaints about the design of 5e. When I want to run something different, really different, I either run a different game or (more often) I create my own bespoke game. But that doesn't mean that 5e is poorly designed; it's well-designed for its use and market.