The keyword is "planned". A planned life extension is not the same as "keeping them airborne because the replacement is late and expensive".
Marines Are Flying Only 60% of F-18 Hornets They Need « Breaking Defense - Defense industry news, analysis and commentary
As for your ‘we all know what the Marines think’ is perfectly appropriate since as their role is, front line, first use, expeditionary force, and, the ground force projection unit of the US Navy, they are likely to be early to any conflict.
Ah, yes, the amphibious landing on a defended coastline, last actually done... well, quite a few years ago. And if you were to do that, an F-35B would be useful as part of a balanced force that could defend itself against the probable threats.