Lo.
I take your points but I believe that the USMC genuinely want to be an all STOVL force and have done so for a very long time (and whether they are right or wrong does not matter in this context). Therefore they are prepared to do/pay whatever is necessary to that end.
Personally I don't think they need stealth and supersonics for their STOVL ops and I suspect some of them would agree but having been gifted the UK aircraft
they are now able to see their way to 2027 without serious 35B availability.
Lucky them as it turned out.