I mean, I would argue that "I just want to do it my way and anything which prevents me from doing it my way is The Worst Thing Ever" is fundamentally a rejection of the concept of game design in the first place. IMO, such people do not want to play games. They want to do the thing they want to do, the game is just a convenient guise for doing what they want to do.
All this is acknowledging is that people have different preferences and tastes about what makes an RPG good at X or Y. RPGs should do what people want them to do and different people want them to different things. Saying that not every RPG needs a rule for X, or that your particular rule for X doesn't do it for them, something isn't a rejection of game design. Some people just prefer that aspect of play to be freeform or they don't like rules for that aspect handled in certain ways (perhaps they want something lighter, crunchier, less abstract, more abstract, etc). That is part of understanding what game design ought to be doing.
Which, yes, if you have a single procedure you want to use and you never ever want to see or hear or even think about anything else, then of course no game can be better or worse, by definition. But games are designed, and design can be a good fit or a poor fit for a specific gameplay goal.
Some people are going to find one system that does everything the way they want, and that is totally fine. But that isn't what I am talking about here. I am talking about how much we tend to glide over taste and preference when talking about whether games are designed well or poorly for X. I agree some games are not a great fit for certain goals. But you have to dive into what people are looking for. You can't remove the opinions of the people you are designing the game for from the equation (including your own). And that is going to mean, some games do X well for certain people, but not for others. Both might be very interested in X, but want to achieve X in different ways.
I do think you can talk about objective things though much more easily. You can measure how long combat takes, you can measure how long prep takes. That is pretty easy stuff to measure and discuss.
A Volkswagen Beetle can be used to tow things, but it's not designed for doing so and will be much harder to use than something that was designed for that purpose. The Socratic Method is great for annoying people and working with a cooperative person to drill down to the deepest substratum of a particular topic (which, as Plato's writing shows, often results in "well we don't really know anything" or "we just sort of assumed this is what it is"), but it's pretty useless for developing your own answers. (I mention this, an abstract thing, to show that the physical analogy is not faulty as a consequence of being physical--abstractions can also be better-suited or worse-suited for particular activities or purposes.)
I do think cars are a very bad analogy. A car either can't tow a certain amount of weight well or it can. And there probably isn't huge variance in opinions on things where someone would pick a beetle over a tow truck for their repo service (if anyone who knows more about towing wants to correct feel free, as I know nothing about it). But take something like combat in RPGs. If you say a game does combat well, that could mean almost anything. One person's definition of a game doing combat well, could be another person's definition of it doing combat poorly. Some people want the mechanics for combat to be crunchy and almost a game unto themselves, some people want light combat that is exciting but doesn't interfere with a fast paced session, some people want combat that connects better to the story, some people want combat that has tactical options but is fairly light, some people want tactical options but with a lot of crunch. Now if the numbers are all messed up and the game is clearly not doing what people want it to, that is a separate issue. But a lot of what we are debating isn't so much whether the game actually does X well, it is about how the posters feel it ought to do X
Yes, you are correct that the sum total of a game should be considered if one is recommending the whole game for any purpose a person might value. But that flatly is not a valid reason to conclude--as has been argued here--that it is objectively false to say that some games are better-suited for a singular specific task than others.
I do think we can talk comparatively. But like I said to Umbran, it gets murky because gamers have idiosyncratic tastes. The thing that might look great to you on paper, may not be great in practice for everyone. And you have to account for personal taste. So yes you can talk about whether a game does politics well, but you also have to account for the fact that people want politics handled in different ways mechanically, and there are people who don't want mechanics for politics (so for them, a game with no rules for politics, does politics well). RPGs are open. They aren't board games. So I just don't think you can measure quality in the same way
An electric mixer is, objectively, better suited to many cooking tasks than stirring things by hand. Some people will still prefer the arduous labor of hand-mixing for various reasons. That doesn't mean the mixer and the spoon cannot possibly be compared for ease-of-use at the specific task of mixing ingredients. It just means that ease-of-use for that purpose isn't the only consideration a person might have in deciding what methods to use.
Again I think these analogies break down. But we would probably both agree that an electric mixer producers a different consistency and end result for making pesto than a mortar and pestle. I've used both methods. I don't one is superior to another. Sometimes I want pesto that has been made in a mortar and pestle, sometimes I want a smoother consistency from a mixer. The same logic can be applied to sandbox. If you have a low prep system, sure that is going to be easier to prep (your prep will be smoother). But for a lot of people 1) they enjoy the prep and 2) they prefer the flavor of a prep heavy game that doesn't do things the way Ironsworn does. They don't have to like it just because Hussar does