I'm not against immutable distro's on principle. I imagine they still have some kinks to iron out, but I haven't looked in on them for a while.
My opinion on these things is; if it's a superior system, then it'll become the new standard, that's always what happens, and the naysayers are largely irrelevant. Just like computers, smart phones, the internet, etc.
In the case of docker I'm already at the point where I no longer think it's necessary. At my current job our stack is JS, PHP and Python. 3 interpreted languages, we then build on Ubuntu and deploy on Ubuntu. I don't think our project really needs docker, even though it does use it. We also have wasm/wasi prepping to eat Docker's lunch.