Test::Harness is not a testing framework. It's a test reporting framework. Test::More (well, Test::Builder) produces output expected to be interpreted by Test::Harness. Test::Unit has its own test reporting framework, though that's really not the point. It could use Test::Harness.

I don't know what you're on about regarding Makefile.PL as you've described exactly what the default Makefile produced actually does.

As for counting tests, why not just run the test file, make sure everything passes, and then change the no_plan option to plan? If that's too much work, set a dependency for Test::Harness 2.x and set no_plan.