All flag officers don't get there without major commands...it's not size of ships or planes or tanks...it's operational commands...and WWII by its nature had a sh*tload of flag officers...4 Admirals, 2 USA Generals and 1 USAF General made it to 5 stars... War on a global scale ramps everything up, especially conventional like that...
Conventional war now days will be short-lived...it's just what follows may or may not be so swell...