One of the most beautiful things about the Alliance system is that it gives you the illusion of significant choice without actually offering a lot of significant choices.
Illusion of choice is basically just as good as actual choice for the vast majority of players. In general, players want to feel like they have as much freedom as possible while designing their character. The Alliance system creates the perception, and as is true in most things in life, perception is all that really matters.
As someone behind desk, though, who has analyzed this system for decades (though, honestly, I was able to see between the lines after only a few years), I know that the actual variance between characters of roughly equal level (ignoring magic items and uber-rituals) is relatively minimal. The reason is because no matter how creative you are, it is basically impossible to push a character significantly higher than the baseline character for a specific class (baseline defined as the "cookie cutter" build with about 10% - 20% of experience spent on roleplay / cornercase racials).
There are a few well known options for pushing the envelope. These includes things like a 1-dot celestial pyramid for non-casters, 3 ranks of alchemy, and a shield for casters. But that list is pretty close to exclusive and none of these options breaks the game so hard that it is hard to estimate the ceiling for power level of a PC of a specific level.
The only real potential problem is heavily underpowered characters. However, since the advent of fluid classing, these characters are almost always a result of intentional focus towards roleplay over combat, rather than poor system mastery. I'm not saying poor system mastery can't make a character hard to judge. There are, for example, a few "sour spots" for build spent ratios for cross class builds (templars, scouts, and adepts). But that type of terrible unintentional terrible build is few and far between.
In short, while the rules technically let you build any character you want, in the vast majority of cases I can gauge relative combat potential just by knowing the level and class of a character. Meaningful variance between characters is incredibly rare, even when their builds look very different on paper. It is very convenient for people who run the game.
-MS
P.S. - Normally I'd be wary of posting something like this to the Alliance boards, because it is the kind of thing that might annoy certain types of players, but I'm pretty sure that just about anyone posting to or reading this forum should be comfortable with this concept.
P.P.S. - In case it wasn't clear, I believe standardized builds are effectively already a part of this game. Furthermore, I believe that nothing I have seen in 2.0 (including paragon paths) changes that statement.