What is the magnitude of delay that you are experiencing? On my system, it is hardly noticeable. I'm guessing it to be somewhere between 50 and 100 milliseconds. I can't imagine so many people complaining about such a small delay. Therefore, I think it must be something else.
1) what infotainment version? (mine is v55.00.753A)
2) what input source? (I mainly use USB flash drive now)
3) when you notice the delay, are you holding down the button or is it just a quick press? This is important, because there will be a delay if you hold the button down. Think of it like a computer keyboard. There will be a second or two delay to switch over to repeating mode.