Notice that the 25th amendment was not designed to bail out politicians who spent four years covering up for their incapacitated President.
It was designed to deal with new information that required immediate action.
Odd given both Wilson and FDR were disabled a long time. Although maybe FDR’s mind wasn’t failing so much as the rest of him. 25th does allow some tweaking of the rules. It should look into that in future post Trumpslide.