On an idle machine quite possibly, though it sounds heavily implementation-specific and application-specific too. Big timeslices matter for CPU bound things.
On a loaded system, a nice -19'd process will get barely any time, politely behaving or not. That's not a bug or anything the scheduler can fix, that's simply the system doing what you told it to.
Unless everything else is 19'ed too, of course.
I agree that priority can be used intelligently, but think it should be up to the sysadmin to raise priorities above average. Leaving it up to the users can cause problems. Leaving it up to the sysadmin can cause problems too, but at least there's just one of them