I do not intend for this question to incite a debate as to the historicity/validity of the account of the Tower of Babel, I am simply interested in seeing how it fits into the framework of modern linguistic understanding.
The account suggests that today, there should be at most a few dozen (if we take the estimate of ~70 languages to be accurate) unrelated language families* whose proto-languages were spoken approximately 4000 years ago.
What linguistic evidence is there to support/oppose the idea that every modern language can be traced back to one of several dozen proto-languages artificially created c. 2000 BCE? How certain are we of each of these pieces of evidence?**
Are there features present in known languages that are surprising to see based on the theory of language evolution? Conversely, are there features which suggest that languages did in fact evolve from simpler early languages? Are there any seemingly vestigial features that reconstructed proto-languages have, which would suggest that they in fact developed from earlier languages?***
There have been several questions on linguistics.SE regarding the seeming complexity of PIE in relation to modern IE languages, though I have not seen a general consensus on this issue (some answers suggest that this is a non-sensical discussion as it is virtually impossible to measure the complexity of a language, while others suggest that modern IE languages are equally complex, though this complexity no longer lies in the morphology****). Are there analogous discussions about other language families?
I apologize if I have brought up too many discussion points for a single question, but I believe they all relate to the main question, and are meant to incite discussion in these directions.
*Some people argue that it actually suggests that all modern languages are genetically related, though I do not believe that is an accurate conclusion as "[confusing] their speech" more directly suggests entirely distinct languages being introduced.
**For example, as I understand it, we are essentially certain that PIE existed, and was spoken approximately 4500-6500 years ago, whereas current evidence for the existence of a Proto-World language is very controversial. Similarly, I've heard of theories about the cyclicity of language typology which it seems are being given serious research, though are not yet entirely accepted.
***An example in English would be pronouns still having grammatical cases (I vs me, etc.).
****Such discussion is mostly related to more analytic languages such as English or the Romance languages (when compared with Latin), or even German, with its disappearing grammatical cases.