Minato was able to have perfect sage mode, why could he only hold it for 10 seconds and naruto could hold it for five minutes?
You don't even know what Minatos sage mode limit is, you don't know his max duration for holding senjutsu, you don't even know if he deactivated it after Madara beat him. You're just making assumptions.
Besides, jiraya can't hold sage mode for even 1 second, yet he has a 5.
I'll make this as clear as possible for you, here's exactly what Fuksaku said:
"UNLESS YA ALREADY POSSESS ENORMOUS AMOUNT OF CHAKRA INSIDE YA, NATURE ENERGY WOULD IUST TAKE OVER RIGHT AWAY".
If minato didn't have enormous chakra, he wouldn't even be able to use sage mode at all whatsoever. It's not about how skilled he is with it, it's iust the fact he can use it. I'm literally quoting the manga to you, but somehow I bet you still won't be able to understand.