And yet, your alternative leaves no way to ever improve anything, and denies the fact that not all designs- or assesments of designs- are of equal merit.
This is not just a matter of opinon. Some people might think that game design is just a thing anyone can do, but it's actually very challenging, and can fail of suceed to varying degrees.
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I agree with the part of your post that I quoted.
I disagree with most of the rest.
4e IS a better balanced game. I will agree with that. If you equate all of design to balance, THEN 4e is a better designed game and it might possibly even follow that it is a better game.
However, there are other elements that were sacrificed in designing 4e. These other elements were also part of the design. Some other elements were amped up, others dampened.
Design is not a linear process from "good" to "bad". It's a blending of a number of considerations and elements, and the whole that is created is the "art" (the synergy of the elements that make up the game...the "whole is greater than the sum of the parts" aspect).
But there's still plenty of "science" in deciding how much of certain elements go into game design. Do we want to model realism in which we have 50 tables with various complicated rules to address each and every eventuality (e.g. AD&D's weapon type versus armor type)? Do we want it less "realistc" and more "smooth to play"? How well a design addresses each sub element can be measured.
What I'm saying is that game design is about making tough choices. Speed versus detail; reality versus simplicity; gritty versus heroic; differentiation versus balance. Note that not all of these are polar opposites, but sometimes are more "complications" For instance, differentiation is not the opposite of balance, though balance is easier to achieve if things fall into a similar template or pattern.
Also, a less quantifiable, but no less important part of game design is fluff design. These are roleplaying games after all. A game with zero fluff, one that only presented rules and no world, no names of races, no feel to it would be poorly designed indeed. One with really bad fluff would be equally poorly designed.
So yes, some games can be called out on being horrible at balance, or realism or whatever else. Some truly horrible games out there can be called out at not being particularly good at any specific measure of good design (poor balance, incoherent and absurd fluff, clunky systems that poorly model reality, etc. etc). But it'd be impossible to find the worst RPG. Yes, there'd be a few contenders, but I doubt there'd be universal agreement on which is worst...just as we can't agree which is best.
In the end, though, you could pick one of those "worst games" that many agree is just awful, and I might think it's the best. I might have a measure that is more important to me, such as the inclination of living teddy bears, which no other game has. D&D is nice, and Call of Cthulu is too, but "Romper Stomper Teddy Bears*" is the cutest...and therefore the best.
If I reify "cutest" as the single design component that matters, and sacrifice all others to make the cutest game out there, then I've made the best. IF (note I'm saying if to make a point here, I don't actually believe this) 4e sacrificed all other elements to become the most balanced, but failed utterly at every other aspect of game design, then "most balanced" and "cutest" rpg are each best at one thing...but they're hardly the "best" rpgs out there.
My point is that, yes we can use factors to weigh quality, but we must understand that no factor is monolithic in importance to game design, and that each and every game balances the factors in different ways. To claim any one game is best is absurd. To claim a game is best at a specific factor might be reasonable, though.
*Romper Stomper Teddy Bears, coming soon to cuteify your daydreams!