Minato barely reacted + evaded kid Obito's Kamui. Kakashi fooled adult Obito's Kamui with his own, and showed more than once feats on par, if not better, with Minato in physical speed and reflexes. His long range Kamui, especially if head sized, is faster than Obito's and a lot more easy to accomplish and unpredictable; thanks to Kakashi's versatility, smartness and timing too, as Kakashi is also far more complete and versatile than Minato overall. Minato is just Hiraishin if he has to fight high level opponents, Kakashi has Raiton mastery, clones mastery, and Kamui as his trump card.
By feats they should be more or less as fast and as top notch in reaction speed too, I'd say Kakashi is physically slightly faster and more reactive with some of his feats in the War Arc, he can also teleport at will between places or the two dimensions (Kamui and real world) with Kamui self warping, but Minato is definitely faster overall thanks to instant Hiraishin, but he also needs to place his seals. They are also two of the smartest shinobi overall but I'd say Kakashi is even smarter, his feats against Obito are more impressing and against Kaguya too (Kakashi was overpowered but his intellect was the same). Minato's Hiraishin speed depends on his kunai and markings, Kakashi can track his kunai and has the reactions and the smartness to give him an hard time with things like Suiton + Raiton combo (electrified field) or Raiton Kage Bunshin, he just needs an instant to warp Minato's head away. In physical speed and reflexes, Kakashi is shown to be at the very least on par with Minato (
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), but seemed even better than Yondaime, if we account that here (
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) Minato is hit two times (in between his sliced arm is also kicked away) without being able to react and Hiraishin away, but Kakashi, even if he could absolutely not be prepared for what happened and was clearly surprised, could activate and execute Kamui in a millisecond, warping away Minato's Rasengan countered by Madara (
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), and that Kakashi, even in an exhausted state, could perceive and mentally react to Juudara's speed (while Minato couldn't, if he could have he would have activated Hiraishin to teleport away).
Kakashi can use at the very least 6-7 Kamui shots (based on his War Arc feats) + Sharingan and other jutsu. So he definitely can take out Minato, especially with diversions like Raiton Kage Bunshin.
Minato has Hiraishin but to land a hit he necessarily needs to outperform Kakashi and touch him or land a seal on him; it's a lot more reliable to think that Kakashi would manage to make him touch a Raiton Kage Bunshin or to time his Kamui to warp away his head. Minato barely evaded Obito's short range Kamui, that is not as fast and not as unpredictable as Kakashi's long range Kamui; remember that Kakashi with long range Kamui could warp head sized objects in the same window of time of Obito's intangibility and of a movement of 5 cm from KCM Naruto, human sized masses so fast that people with full knowledge and top notch reflexes boosted by Mangekyo Sharingan and Rinnegan vision couldn't perceive the warping happening in front of their eyes (namely Obito ofc), giant sized masses even faster than the instant summon of the Summoning Jutsu. Even Minato couldn't perceive what happened when Kakashi used Kamui on the Gedo Mazo while Madara was summoning it... I'b bet on Kakashi for the win.
