Their validity, or even their level of quality as a culture, is not necessarily measured by their ability to invent writing. We are not automatically better than them just because of that, and we certainly don't have the right to pass them off as savages.

They don’t have time to engage in any sort of philosophy.

They did. Columbus made contact with a very sophisticated culture that was soon wiped out by disease, and effectively entered a dark age from which it never recovered.

We normally divide human philosophy into Western and Eastern types. There's some evidence that on the American continents, there was a third independently developed branch of philosophy. It was all but lost, with only oral retellings remaining.