[unqueued]

Both Finder and explorer.exe will mung mtimes from casual browsing, usually due to metadata updates. It is a common enough problem that there are utilities to bind mtimes to files.

IMO mtime the de-facto file timetsamp metadata, since it is most widely supported. The other file timestamp metadata I found were not as useful or portable.

And people use git for storing more than just source code.

I personally find it very useful to be able to clone my podcast index and have accurate timestamps not just from the commit, but from the file itself.

Timestamps can be important for a collections of files, but they are fragile and often an afterthought.