Daz said:
I don't like the design assumption that you need specific, abstract roles or else the players step on each others toes.
Neither did Steve Kenson when he designed True20.

True20 has roles to allow players to build a character that does the in-story job they want to do (their role in the tale) while still remaining balanced with the other members of the party. The roles aren't there to limit, or prevent toe stepping (nothing stops you from having a party of six experts), they are there to make character generation faster and easier than it is in systems like GURPS or M&M.
Daz said:
Here's an example. By default, it looks like true20 disallows anyone but adepts from taking magical effects. But what if I want to emulate Avatar, where only expert martial artists can produce such effects.
What about it?
a) There is a fan-developed conversion for Avatar on the Settings portion of the True20 forums.
b) There is a feat in the True20 companion developed for
exactly that desire.
c) There is no reason Adept power usage can't be advanced martial arts techniques. This leads to the interesting encounter of a purely physical martial artist (mostly Warrior) versus a much more mystical martial artist (mostly Adept). If both play to their strengths then it should be an even match.
Daz said:
There is still a potential for character variety, but the true20 system doesn't really allow for the essential character concept.
That particular example is probably very easy to overcome, but my point is that roles like warrior, expert and adept (or even worse defender, striker, leader and controller) limit character creation rather than help a game move along.
Right. You appear to be projecting the flaws of every Class-based system, ever, onto the True20 Roles. You appear to be doing so without having actually looked at the True20 Roles. (If my assumptions are in error then please correct me.)
The only 'limitation' on the roles is that certain abilities that only make sense for combat experts, skill masters, or mystic delvers are only available to those types of characters. There are a few exceptions, where something that could reasonably be available to anyone are only available to one role (Sneak Attack leaps to mind), but those exceptions are limited for game balance purposes; the limitation creates a cost for certain powerful combinations and gives roles that might be weak in a specific area some unique options that allow them to shine even outside their primary role.
I hope you'll take a look at True20, and judge the system by what is there and not based upon any class-based system. It's one of my favorite d20 variants, and one of my favorite game systems, so I want people to like it. However, no one can be forced to like something, so I won't try to push you into liking it, and I hope no one else tries to force you into liking it.
(Yes, I'm not classifying True20 as a class-based system. That's intentional. Those familiar with my arguments on the topic will know why. Roles aren't classes, they are Roles; they have different assumptions, different mechanics, and a different purpose within the game than classes do.)