Hello,
Reading @Alejandro's answer, it looks like Random is a namespace, designed to welcome some future random-related APIs, including generators: Random.xorshift128Plus, etc.
Couldn't we honor this design decision and envisioned use cases, and in the same time address the concern expressed by this pitch? Renaming Random.default to Random.defaultGenerator could work. The type of Random.defaultGenerator would be DefaultRandomNumberGenerator. Random itself would be an empty enum, the only namespace-like construct we have so far.