empty new project contains too many useless packages,
and its slow to remove them from Package manager one by one:

TODO,
new project window

• checkbox to allow [ ] use minimal packages? (just visual studio?)
• or, separate packages list popup where you can select and toggle packages? (and it remembers those selections next time)
• how to handle separate unity versions, have different packages..

OR,

• option to replace and edit default packages PER unity installation... this might actually easier / better. (*But requires admin access to modify installation directory files)

OR2,

• Global package "blacklist", with button to "remove blacklisted default packages from all installations" ?

OR3,

• when creating new project, you select your own template (but requires you to first create own template.. maybe that needs simple template editor then.. but problem with unity version changes.. packages will change)

looks like the default manifest is at:
Editor\Data\Resources\PackageManager\Editor\manifest.json
and it allows setting if package is default?