The first bit in bold: exactly, they all take 'the same courses'. The courses mean next to nothing. Do you really think taking a few exams after a long playing career (in your words, 'immersed themselves in the game since they were young') is going to make any appreciable difference to an ex-professionals chances of becoming a good manager? Know all the man-management skills? Again, theoretical knowledge of 'man-management' is virtually useless. It takes a certain personality to be a successful manager. This simply can't be taught, and it's the managers personality/charisma/leadership qualities that will make him a good 'man-manager' or not. Page/Edinburgh/Hasselbaink didn't have 'it', and though it's early on in his reign, Austin appears to have 'it' in spades.
The second bit in bold: You can not really believe that if a manager has decent budget or simply a 'lucky season' they will 'do OK'. This is complete nonsense IMO. Having a decent budget gives you an advantage but it is far from a given that a decent budget will guarantee any kind of success. Both Guardiola and Mourinho had huge budgets last season, both were aiming to win the title. One team generally played a defensive game, with a more direct attacking style, while one played an open possession style of play. Both managers have very different personalities and man-management approaches. Essentially both have stamped their personality, their fingerprint, on their team. If the managers had been hired by the other club, then the styles of play and most likely end of season result would have been reversed. The managers are everything to these teams current differing levels of success IMO.
You say the courses mean next to nothing but they are not 'a few exams'. For example Uefa level 5 cost around £9,000 and takes either 30 days intensive or 18 months and then there is no guarantee of passing, many fail. In order to apply for that you would need level UEFA level 4 which is around £3,500 and 18 days. You need UEFA level 3 to apply for that and so it continues.
The problem for any aspiring manager has after going through all that everyone else has passed the same extensive courses. So you can imagine how frustrating it must be for a manager to have to listen to some fan who details exactly where he went wrong just because he 'played a bit'.
As for man management, trust me they go on plenty of courses to hone that particular skill. Anyone that's been in any type of management job at a sizeable company knows the courses and football managers are no exception.
It seems as if you have really bought into the new cult of manager that's recently portrayed by the media. They do this to add personality to games in a similar way to the managers at WWE. Beneath the exaggerated personas displayed by Klopp, Mourninho Ranieri etc is a person that knows the job inside out and the interviews are just part of the circus. I would suggest virtually all managers are at very similar skill levels which leaves the money and luck to differentiate them. This would explain why Raneiri was able to guide Leicester to the Premiership and was sacked the next season to give one example of many similar successes then seemingly strange failures.
If you don't agree then why is it that each time a club goes for a manager it's from the same pool of ex-managers?