People who have successfully worked in management and leadership positions in their own professions over many years can quickly deduce that Corbyn does not possess strong ‘leadership qualities’.
Remember that he was a backbencher for decades, rebelled against the whip more than anyone else in recent memory, and finally became the party leader half by accident. He does not know how to compromise, he does not know how to calculate, and he does not even particularly know how to influence. He’s happily been a lone voice in the Commons and so has never had to teach himself how to do any of these things well - they all take years of trial & error to perfect, especially against the teeming backdrop of British public life.
Jeremy comes across as strikingly similar to the useless line managers that many of us have often found ourselves working alongside - in that he makes decisions too slowly, he struggles to clearly articulate his goals and beliefs in front of an audience, he lacks charisma, he avoids uncomfortable conversations and dodges the discussion of difficult topics like the plague (he didn’t speak to Luciana Berger for 14 months before she resigned - when a lot of the issues there could have been solved through an open & honest private chat), and most notably he is unable to unite his immediate subordinates in pursuit of a single vision and purpose.
This is not media indoctrination - these aforementioned traits are all plainly observable, and evidenced by Corbyn-Labour’s constant division, instability, and their consistently poor performance in the polls.
Look up the “Peter Principle”. It is Jeremy personified.