There's no reason this needs to be the case: slider elements could trap the cursor and give realtime feedback of input.
The iPad Pro trackpad does this with all UI elements and I believe it's an important step for UX.
I personally like having opacity sliders as well. They provide a nice visual representation of the state that’s easier to parse than reading a number, and you can also do things like set 100% with a single click. Layer opacity is important enough that it should have a text field, a draggable value with a modifier, and a slider.
The other main point of the article is that these tools don’t seem to even realise their precision sucks.
Thanks for the great article, the images you created are especially fantastic.
Edit: my friend just checked and Clip Studio Paint also has 0-100 with no decimal support. Crazy that it's ubiquitous.
Interestingly, Acorn can show the full 0-255 range.