Here's one of the things I like about the R/C/T style, the math regarding options.
Let's say 5E mainly has R/C and theme is only an afterthought, not really an equal option. If we say 12 races and 17 classes that's 218 unique combinations. Not bad.
But if R/C/T are equal choices, things change. Let's say we reduce races to 10. We reduce classes to 10 because we're moving some of that to themes. Then for themes we have 10 choices as well. That makes 1,000 unique combinations!
The more you split up options into smaller independent packages, the more outcomes there are. The more outcomes there are, the more the game naturally settles into the impression of balance which is just as important as actual mechanical balance. Even better, this doesn't increase complexity. Choosing from 3 lists of 10 choices is not any harder than choosing from 2 lists of 12/17 choices.
Let's say 5E mainly has R/C and theme is only an afterthought, not really an equal option. If we say 12 races and 17 classes that's 218 unique combinations. Not bad.
But if R/C/T are equal choices, things change. Let's say we reduce races to 10. We reduce classes to 10 because we're moving some of that to themes. Then for themes we have 10 choices as well. That makes 1,000 unique combinations!
The more you split up options into smaller independent packages, the more outcomes there are. The more outcomes there are, the more the game naturally settles into the impression of balance which is just as important as actual mechanical balance. Even better, this doesn't increase complexity. Choosing from 3 lists of 10 choices is not any harder than choosing from 2 lists of 12/17 choices.