The problem of “shadows” is how many EVs is that ?
I don’t have strong opinions, Lab just sucks. It was never intended to be a color working space, but only a color description space, used for example as a connexion space for ICC profiles. Do you see any other software using Lab as their default pixel pushing space ? That’s right, nobody does that. So I don’t know what the hype was with Lab at the early stages of dt (maybe it’s because it’s a very large space, or it looks cool to be able to adjust luminance separately from color, or maybe because 50% L means middle grey, when it’s 18% or so in linear spaces), and I guess it didn’t show big issues when cameras had about the same dynamic range as the 8 bits JPG output (so camera raw → JPEG was pretty much straightforward). But now, cameras have almost twice the dynamic range of JPEG, and so does film, thus you have to squeeze the pixels in there and tonemap like crazy, and Lab clearly shows its limits here.
So the pipeline in dt should look like RGB all along. Lab creates more problems than the ones it tries to solve. People tell me they get better results with filmic and color balance than they did before, and are now able to recover easily pictures condemned to garbage before… Well, both work in RGB space. That might be a clue. Also you see above the difference between Lab shadows/highlights and RGB tone equalizer when you push both far away: one behaves, the other fails.
Now, Lab works for things like equalizer and local contrast, although I wonder what XYZ would do there, but that’s about all.