Okay, I hear you. I don't think the issue is quite as bad as you make it out to be, though. I'd argue that the only real place where there is significant overlap is themes and backgrounds. I would agree with you, actually, that we probably don't need both. But I prefer themes, because I think of themes as simply better-implemented, more mechanically interesting backgrounds. Next time I run a campaign, I might disallow backgrounds, since themes fill that niche so much better.@Kinneus That was a great response to the idea of narrative vagueness vs narrative specifics...
In case you missed it, my post actually was about *design space* vagueness leading to confusing/arbitrary overlap. Hence my silly examples.
Background, race, class, paragon path - these all have distinct roles in defining a character. You're probably not going to confuse a background for a class, for example. Themes are a bit stickier.
At first blush themes independent of setting are rather amorphous beasts. "Templar" and "escaped slave" make sense because they describe a character's social status in a brutal hierarchy and they provide an extra boost in a low-magic setting.
But what does "explorer" have in common with "alchemist" to justify belonging together as themes?
Seriously, take backgrounds out of the equation, and I think all the confusion and overlap melts away. Ranger/Battlefield Archer/Explorer makes sense to me. Sure, they're similiar, but still distinct enough that "Explorer" adds some particular, unique flavor to the character. "Alchemist" or "Ordained Priest" even more so.