You're basically saying web browsers and other applications (including IDEs, chat apps, etc) should remove support for tabs and rely on WMs providing tab functionality. Some of tiling managers you mentioned that I'm familiar with don't have any functionality I would be happy replacing browser tabs with.
> If you have want to have 100 tabs open, you should be using bookmarks or history instead of tabs.
Bookmarks and history have very different UX from tabs, they are clunky to use and I would never prefer them to opening 100 tabs, sorry.
> If you want to have different workspaces, profiles, or so on, use your window manager's workspaces
These workspaces don't enable separation of cookies and other state, they have a very different use case to browser workspaces.
> If you have want to have 100 tabs open, you should be using bookmarks or history instead of tabs.
Bookmarks and history have very different UX from tabs, they are clunky to use and I would never prefer them to opening 100 tabs, sorry.
> If you want to have different workspaces, profiles, or so on, use your window manager's workspaces
These workspaces don't enable separation of cookies and other state, they have a very different use case to browser workspaces.