>>48535377new islands to explore > fighting a bunch of rando trainers
Only bad things in FRLG were lack of Gen 2 and 3 'mons and no trading with Hoenn, however both are unlocked in the post-game.
Let's Go has neither, even in post-game.
Unless you count Alolan Forms, Megas and Meltan/Melmetal.
But still far less than you would expect for a Gen 7 game.