I'd say Ctrl+W is just a terrible shortcut for closing a tab.

It's right near Ctrl+Q, which usually quits an application.

While Q is mnemonic, W is not.

It's too ergonomic and requires very little wrist movement for such a destructive action.

I understand your pain, but I blame the author of this weird convention for the "close tab" action, whoever they are

I think it came from the close window shortcut on Windows back when browsers didn't have tabs.