In the same sense that a Yeti would be out of place in a desert, so too would it be weird to see certain races, classes, monsters, and even mechanics in this setting.
Well, yeah, I agree on the surface anyway.

However, the yeti-in-a-desert thing is a thematic disconnect that, as world-builder, it's your job to discourage/eliminate. Races, likewise. I don't have raptorans, catfolk or elves in Patria. Thematic disconnect.

The point where these things fall apart isn't "Well, a yeti is too powerful..." or "Eh, that +2 to Illusion DC's that Gnomes have just doesn't do it for me..." It's the in-world visible things. If you look at the yeti as a statblock, take away all the thematic references and just see a CR, AC and the like, does it work in a desert?

Well, yeah. There's nothing wrong with it's stats. Those are in-world invisible.

Classes kinda fit this too. From an in-world standpoint, they're somewhat hard to detect. It's not easy to tell whether the screaming dude with an axe is a Fighter, Ranger, OA Samurai, Barbarian, Sorcadin Gish, Duskblade... If you just look at what a class can do, you'll find it's kinda hard to ban classes flat-out.

For example, I had a hard time with Psions, most because of the fluff. Come on, making stuff out of crystals and extoplasm? Really? Please. Then, I looked harder at what they actuall do as a class.

"Oh... elemental blasting? That's ok. Messing with people's minds? Fine. Making a monster-type thing with a form not determined in any way beyond the picture that accompanies it? Sure, sure, call it a totem animal."

I closed off a couple powers (mostly time-screwing things and the Astral Traveler line) and called it good.

The mechanics, the power point system, the augmentations, the chassis, all were fine. It was the fluff I had an issue with and the fluff that I changed.

What about mechanics?

These, by very definition, don't exist in your world. Nobody sees a sword and goes, "ah, yes, a 1d8 slashing medium-class weapon!". No character has ever rolled a nat 1. They may have failed spectacularly, but this whole dice concept is foreign to them. As a builder of fluff, primarily, and the mechanics that support it, it makes little sense for you to, in that capacity, limit what goes on behind the scenes. Mechanics and fluff should support each other, but still be distinct.

So across all this, what did I take out of Patria?

Primarily thematic sticking points. Races that didn't work, powers that were out of place, abilities that didn't mesh.

What stayed?

The opportunities for characters to customize their characters as they see fit, barring any fluff-based square pegs in round holes.

I see your point that being streamlined is good, but honestly, if someone's looking for a streamlined system, 3.5 isn't the best choice.

[/rant]

Sorry if I seem kinda combative, but with important things like this that really influence gameplay it's important to put them to a test to make sure they're the right choice.