This should really be documented. An issue that keeps popping up is conflicts with third party dll's that Unity keeps pulling in, and people don't know how to solve it correctly, resorting to painful assembly def solutions that aren't really solutions. Also, that the package manager doesn't show the entire dependency chain is not helpful when people hit an issue here. You have to know to go look in PackageCache to see what's really installed.
Hi @snacktime, Which version of Unity are you using? In the latest version of Unity, there is now an *Advanced -> Show Dependencies* menu in the Package Manager UI. When this is enabled, all packages are listed (root *and* transitive dependencies). Regards, Pascal