> Professional Managerial Class (college -> management being the norm)

This isn't the norm in most STEM industries anymore.

Most of us started off as IC-level engineers before either beung given progressively more responsibility and/or being sponsored by our employees to participate in a PTMBA like Wharton, Booth, Fuqua, or Haas.

Networking and hustling did ofc play a role, but lacking domain experience would limit how high you could climb.