It's potentially that I'm using a 2019 MPB, but I can absolutely touch and slide to change volume immediately. Just press and slide on the icon for volume or brightness.
Also pro-tip: you can change the buttons that show up in the touch bar. Settings > Keyboard > Customize Control Strip. I swapped out Siri for a "Sleep" button, which is super convenient when I walk away from my desk.
On my 2017 with Catalina there is an animation that occurs to show the volume slider. Any sliding of your finger that occurs before the animation completes is definitively ignored. Additionally, there is a significant delay before the animation even starts.
I just timed it at ~580 milliseconds, more than half a second from finger hitting the bar to the time when it stops ignoring touch input. It's easy to slide your finger more than the entire length of the volume bar in that time. It's absurdly bad. It would be weird and pretty lame if they fixed this only on newer models.
Also pro-tip: you can change the buttons that show up in the touch bar. Settings > Keyboard > Customize Control Strip. I swapped out Siri for a "Sleep" button, which is super convenient when I walk away from my desk.