Interesting post.Disagree, though allow me to frame. In any mechanically light situation, such as a social interaction, exploration or meta-game plot realisation (you know, when you solve the mystery or connect the dots), characters can shine independent of the system used to create them.
<snip>
In a mechanically heavy situation, and you can't get much more mechanically heavy than 4E combat (3E comes a close second!), the way the characters are built makes a huge difference in their ability to shine. When built similarly, following the same structure, not differing too much in terms of defences and other numbers, it's difficult to shine in a unique way, to do something that nobody else could do, to solve a problem in a way that only you can. What it does instead is encourage strong teamwork, and synergy
I think I have a different view on two points. First, I'm not sure about the "mechanically light" thing - a lot of social interaction in D&D is (in a certain sense, at least) mechanically heavy (eg the use of a Charm or Suggestion spell), and I'm not sure "mechanically light" fits well with "balancing classes around the three pillars".
Second, I'm not sure that similar structure in a mechanically heavy domain precludes unique shining. It seems to depend heavily on what the content of the structure is.
But happy to hear more from you about what I'm missing in the above, or where I've gone wrong!