The only thing they have in common is package.json, but even then they can interpret things differently, such as workspaces.
And then node_modules, which packages should not rely on but do, forcing many other tools into compatibility mode which often takes an install take a very long time.
Yes, the node ecosystem is very healthy.
Isn't the point of node_modules to house ... dependencies? I'm confused as to what you're getting at here.
There are ways to not use node_modules, by using newer Yarns for example.
My point was that if you use yarn2 in pmp mode, and you have a dependencies that depends on the node_modules layout being at the same level as package.json, than even if your package manager doesn't not need or use node_modules, it must emulate it so the dependencies can find their files.
Once you've landed on a package manager that does use it, wouldn't you continue to use that?