If you look through the good coaches, there is as many, if not more that were battlers/honest toilers as players rather than naturally gifted players Malthouse, hafey and sheedy come to mind as examples
To be a good coach you need to have an understanding of the game, be a good communicator, a good motivator and need to be able to relate to the players for whom things just dont come naturally.
Being naturally gifted as a player does not necessary mean you will have these attributes, and if you are a simplton then it makes it less likely you would be a good coach.