The amount of chakra needed for FTG is directly proportionate to the size of the thing being teleported. So if it's teleporting ones own self, then they need chakra equivalent to teleporting the size of an entire human. Which isn't really small, the fact that ftg is spammed means the user itself has loads of chakra.
Besides, it's an S rank jutsu. It was always going to be hard to learn. The user is acting like its some basic jutsu that Naruto should know lol. Where is Narutos knowledge of sealing jutsu, you'd need to understand sealing jutsu to the fullest, because it requires your own seal. Naruto isn't that smart, all his techniques revolve around concepts already established and spoon fed to him. Complex jutsu such as sealing techniques he's never shown knowledge in. If it takes 3 special Jonin to perform a single teleport, then you know it's a crazy technique to master.