I thought you said you wanted him to explain his statement about high speed maneuverability? 
I asked him to explain in quantifiable, verifiable terms. He has yet to do that.
Claiming "no high speed maneuverability" is not only false, it's also entirely subjective and useless in the course of a discussion such as this. Had he actually pulled the plane performance statistics, he'd find that the Ki-84 falls squarely in the middle of high-speed plane performance and is actually very average.
Further, it's not a lack of high-speed maneuverability that makes the aircraft appear to turn poorly, but rather the fact that the Ki does not give up E easily. This makes it hard to slow down the aircraft to its optimal turning airspeed because it doesn't bleed very much E in turns. However, this is actually a desired trait in turnfighting aircraft... and the aircraft would not handle well at all if it didn't retain its E in this manner. Therefore, it actually has good high speed maneuverability, it simply doesn't bleed E quickly enough to use most overshoot tactics.
Complaining about this is akin to complaining that a D9 has horrible turning at low speed; the D9 has horrible turning at all speeds (and if you took time to generate for the plane, you'd find it's 3rd or 4th worst-turning aircraft in the game). However, it dumps speed so quickly that it can cause overshoots easily, as well as perform some stall maneuvers, giving the illusion it turns well because you can drop airspeed quickly at high speed. At low speed, you have no excess E to drop and its poor turning becomes apparent. This is a side effect of high wing-loading, just as a lack of speed loss is a side-effect of low-wing-loading on aircraft like the Ki-84.
All of that said, I'm not sure why people are trying to make the Ki out to be some kind of skilled plane to fly by claiming it has horrible performance in certain realms of flight. It's almost laughable, as if they're trying to preemptively save their man card. If people actually cared about planes that took skill to fly, they'd be in P-40's. This is just another thread where people are trying to make excuses for their plane of choice, as we all do; the only difference here is that it seems the people that fly the Ki can't even properly explain their plane performance.
Have you ever recorded a kill in the MA in a Ki-84?
Yes, but even if I hadn't, it has nothing to do with someone else having to verify their claims.
