Your theory works just fine under the assumption that all core mechanics are more or less serviceable and have little effect on the enjoyment of the game in question. Given the history of RPGs, wherein core mechanics have always consisted of a small group of a handful of original systems (here defined as systems that are the first of their kind and recognizably distinct from other first generation systems) and a large collection of variants that are similar in general structure but different in details to some degree* this is a reasonable assumption. However, the group of original systems (as opposed to variants) to which we’re exposed is very small, perhaps a half dozen to a dozen. This is not to say that there aren’t MANY original systems out there, just that most aren’t high visibility. Of the low visibility original systems, some (like Dogs) are pure genious and are only low visibility because of issues nonrelated to system. However, Statisticly speaking, a good number of these systems must be more or less trash, sentenced to permanent exile from the spotlight because they are untenable.

That in mind, The character sheet is a great place to start your inspection of a game. Just don’t take it to the cashier before takeing a quick look at the core mechanic.

*For example, we would say that 4th edition Shadowrun and the Whitewolf system are variants of one another with very little difference except the size of the die in question.