On it
edit: So I can't do a video right now, but as a quick and dirty comparison, I used two youtube videos at 0.25% speed -
https://youtu.be/QoB1pKJjAAc?t=161 (GameCube, single fire into charge shot begins just after 2:42)
https://youtu.be/fn9bqNVu_tA?t=173 (Switch, triple shot into charge shot begins during 2:54)
I timed the two shots to one another by going frame by frame, basically. Started 'em up at the same time... and what I'm seeing suggests that they're either the exact same speed, or that firing a charge shot is slightly faster on Switch. (I also think that time to full charge is also slightly faster on Switch, but I'm not entirely sure.)
This is by no means conclusive or anything, lol - someone with some solid capture hardware who can measure button press latency will need to put this to the test - but at the very least, I think I can confirm that firing a charge shot on Switch is slower than firing a charge shot on GameCube - despite the preceding triple shot.