Yes, part of the issue is that sublime doesn't have or expose the notion of current working directory (CWD). That notion partially conflicts with the idea of "project folders"; since you can have >1 project folder, which is the CWD? One solution would be to have the CWD for a buffer's editing session to be it's containing project folder, but that has issues when the file is in >1 project folder, or one project folder is nested in another.
Another option is to have the CWD as the directory that sublime is launched from. Some editors have the notion of CWD, and some have a console/commandline which allows it to be changed with a CD command.
In Sublime's "intuitive-land", I would favour the approach of the CWD being containing project folder, with some caveats for the multiple project folder scenario above. The CWD for a file that doesn't belong to a project folder would be the launch dir, and it would be nice to have a Sublime console command to change/show the CWD as well.