FTG is not the speed of light. The speed of light is finite.
FTG is instant, that's 100000000000000000000000000000000000000000000000000000000.....000000000 km/second, whereas the speed of light has a limit.
Obito is faster than Minato in footspeed, no doubt about that, but I doubt he is faster than BM Naruto -BASED ON HIS LATEST FEAT-.
By hype, he should definitely be faster.
If Kyuubi makes Naruto so fast it only makes sense for the Juubi to do the same for Obito.