(1st paragraph)
This is why I said I believe Kishi amped him up. In Kishi's world, yeah he's strong. But in Kishi's world, Rock Lee was did better in 1-2 years than in 3-4. A bunch of edos and Senju-empowered-zetsu lose to the less numbered and out-powered ninja world. Juubi/Juubito lost to the ninja Alliance. Madaara didn't kill the kages. Neji didn't air palm / rotation the spike instead of jumping to it. Despite being on/close to Kakshi and Guy and K11 levels of rank, they all are academy level in battle. And I could on and on, those are just off the top of my head. Kishi's world isn't always reasonable, cause he's human like the rest of us.
And honestly, have we forgotten the speed of Raikage? Have we forgotten??? The dude can bltiz reasonably anyone. At the speed the anime/manga showed him moving, it is literally impossible for Minato to have taken out a kunai, and thrown it before A moves like 1cm. Heck, to move that fast the kunai owuld've had to like burn from friction. I don't have time to get down into it, but really, it's noteworthy Minato could even see him and react at all, and I'm personally (just my opinion) am convinced that the only reason he did what he did was due to plot-speed-boost. And even if by some miracle, assuming Minato can move his hands faster than A can move 1cm, a kunai isn't faster than A.
(2nd paragraph)
The ninja are faster than kunai- at least most of them. And any analytical ninja should be able to be wary of the kunai 100% of the time, and stay from it's radius. My point is really this: FTG itself isn't that bad. What maes it bad is when a genius like Minato has it. What makes it OP is when he has reaction speed that [in my opinion] literally isn't real, and everyone else seems to dumb down to it.
But hey you know what, maybe I'm wrong

It was just my 2cents lol. Thanks for the intelligent response btw. I didn't structure mine to well as I'm rushing to bed, but oh well :I