"Make [a slider] bigger while the mouse button is held down, and warp the mouse so that when you let go you pick up where you left off" has been a solved problem for decades.
And with traditional toolkits (i.e. not HTML) it will even be fast.
I was able to debug and fix someone's MainStage patch last night over SMS when they sent me pictures of their screen, where all the knobs were visible.
Being able to see the full state of the thing is important. Hiding it behind interactions is just as bad as hiding it behind menus.
Sidenote, you have to do this on native because pointer lock/warp is not universally supported in web browsers.
As someone who regularly uses DAWs, this sounds like terrible UX
It's not all about the interaction, but also the visual representation which can be much finer and granular in small spaces with a knob.
I can make a 16x16px knob where you can see almost the entire 320° of the range.
It's also easier to see fractions, such as 1/2, 1/3 or 1/4.
Sliders, especially in 16px possess none of those.