Let me define speed for you:
1. Physics The rate or a measure of the rate of motion, especially:
a. Distance traveled divided by the time of travel.
b. The limit of this quotient as the time of travel becomes vanishingly small; the first derivative of distance with respect to time.
c. The magnitude of a velocity.
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To sum all that into one sentence, speed is how fast you get from point A to point B.....it doesn't matter how you get from one point to the other and who doesn't use things to help their speed....gai and lee use gates, raikage uses lightning shield, and uchihas use sharingan for better reflex.....so Minato IS the fastest
I could drive a car to my destination.....but does that make me faster than an Olympic runner? no
Lightning release and gates, etc is like say the speed boost version of steroids....yeah it's still cheating but it's a part of them
FTG is like a car, all those speed boosts are like steroids
I have terrible analogies I know