Could just be bad timing?

the USMC takes up a big chunk of the Land Warfare pie. Who’s going to fill that vacuum, the Army? Is the Army ready to do that?

Unfortunately, IMO, USMC has filled that vacuum since 1945 because the Joint Chiefs saw it as supporting a smaller US Army following WWII. (Same in WWI, BTW.) I think that was wrong, but it became the norm. USMC maintained its combined arms, air/ground task force and Amphibious Expeditionary (they always had at least a Battalion Landing Team at sea) concept while also filling out its Land Army tasks.

Korea, Vietnam, Kuwait, Iraq and Afghanistan had USMC in their Land Army task, and just maybe the Joint Chiefs started thinking this was a bit redundant? They also started believing that Special Ops was going to be far more important in future conflicts. IMO, Ukraine's slug fest with Russia should change the US military and USMC structure going forward, and possibly do a 180 when it comes to Marine heavy weapons.

Harvey