I agree with all this.
Toward the end of the war, the Japanese were producing some very competent fighters that equaled or exceeded some of the performance attritbutes of the F6F. These were fighters that were just being placed into service in 1945 when the F6F had been fighting since mid 1943. The Japanese never had enough of them, and certainly didn't have the pilots that could exploit the capabilities of their new planes.
The F6F was the right plane at the right time. Easy to fly, fast enough, rugged as hell, low stall speed, great deck handling characteristics. The Navy had a metric sh*t-load of them, and a huge quantity of pilots able to fly them. It met the Navy's need until the end of the war. So there was no need, like the Germans and Japanese had, to rush better and better planes into service. But there is no denying the F6F was obsolete in August 1944 when the first XF8F flew. Indeed, its obselence was anticipated in 1943 when the requirement for the F8F was issued.
As far as the F6F not remaining in service after the war, except in the roles you mentioned - It's true. There was no future in the F6F except as a reserve aircraft, trainer, or drone. It shouldn't have remained in service. Its replacement, the F8F, was already a developed fighter and making its way to more and more squadrons. The F8F is arguably the best piston engined fighter to see service with any nation. But even it couldn't compete with the F4U in meeting the Navy's need. The F4U-4 was as fast or faster, carried a larger load further.
Maybe Grumman didn't know it then, but once the F4U flew, the handwriting was on the wall for Grumman piston engined fighters.