That's a pretty high success rate for large, long-lasting literary civilizations.

Sorry, 'emergence' was probably the wrong word. 'Persistence' or 'development' is probably more to the point. The Chinese got unlucky with that madman of an emperor, but in any case I don't think anything coming from either the Indian or the Chinese tradition can really be compared to the European/Greek tradition after Aristotle. I'm not extremely confident in that judgement. My exposure to Indian and Chinese philosophy is not trivial, but obviously not extensive. I'd be pretty surprised to find that there's something in the Chinese or Indian tradition, at any period, that's anywhere in the ballpark of Kant, or even an early medieval commentary on Aristotle.

philosophy-like things probably arise frequently and just aren't recorded as well in most cultures.

Maybe. I expect there's going to be a close enough relationship between literacy and philosophy that this isn't a safe claim.

since sophists did a lot to weaken early Chinese and Indian thought as forerunners to science and rationalism.

Can you elaborate on that?

And, as I noted, Plato and Aristotle founded Western philosophy about as much as Ronald Reagan invented liberal democracy. In both cases, the 'founder' in question appears some 200 years late.

Maybe we disagree about Ronald Reagan, but it seems to me that Plato and Aristotle marked a radical upswing in sophistication. And both did found philosophy in many ways: everything that preceded them was comparatively narrow in scope, and generally lacked any systematic or thoughtful approach to ethics, logic, epistemology, etc.