A retired Naval officer posted this on Quora. I haven’t had a chance to fact check it, but I assume it is correct.
CJCS: Gen Dan Caine USAF (ROTC, VMI)
VCJCS: Gen Chris Mahoney USMC (OCS, Holy Cross)
COS Army: Gen Christopher Laneve (ROTC, Arizona)
COS Air Force: Gen Ken Wilsbach (ROTC, U of Florida)
Chief of Naval Operations: Adm Daryl Caudle (ROTC, NC State)
Commandant Marine Corps: Gen Eric Smith (ROTC, Texas A&M)
Chief of Space Operations: Gen Chance Saltzman (ROTC, Boston University)
Chief of the National Guard Bureau: Gen Steven Nordhaus (USAFA)
Assuming this is correct, it would dispel the notion that being a service academy grad is necessarily the ticket to the upper echelons of the armed forces.
Only the Chief of the National Guard Bureau is an academy grad (Air Force).
Six are ROTC, and one is OCS.