I wonder it would make more sense that job would be blocking other jobs not only if it is running, but if it is queued (blocked for instance, or waiting for empty slot).

If I set that job A blocks job B and B blocks C, and run A, then B, and then C, I would expect that job C would execute only after B unblocks itself, and finishes. The job C however starts immediately because job B does not run at the time (is blocked by A).