This would be the best way to show kakashi is still powerful, if could control white chakra he would be called the white flash. I mean if genma could use the jutsu with 2 other fodders why not kakashi by himself ?he'd be the only ALIVE person that can use FTG by himself and the people using the stamina excuse remember Sharingan takes a lot of chakra from Kakashi and without that burden he could use it more effectively plus it would allow him to use Lightning Blade with FTG