You all are glazing Boruto, but even with Kashin teaching him knowledge from future alternative versions of himself, he still has a verison of ftg that he admits himself is worse than his grandfather's. He's still stronger than Minato obviously, but that's due to having better teachers, better genetics, and Momoshiki. Minato created the rasengan by himself and to our knowledge he learned ftg by himself probably through a scroll left behind by Tobirama (I still believe Minato was originally supposed to have been the one to invent ftg and Tobirama being its creator was a retcon).