I do think they should have a more obvious warning that the current directory is untrusted, right now the little green warning in the corner is way too unobtrusive and will result in many people having the same issue as you.
The latest x86_64 Linux build is 136MB. (https://zed.dev/docs/linux#downloading-manually)
As for your list of grievances, they all seem to boil down to the respective LSPs not doing their job? Does Ctrl-Alt-l (lowercase L, not Shift+i) include the language's server in the context menu, and are there any errors reported for it if it does?
That is the part that makes the space heater