Being a good player is not a criteria to becoming a good coach. In fact, there's a trend of most average players who turn out to be great managers of their time. The likes of Sir Alex Ferguson, Pep Guardiola, Conte, Arsene Wenger where not really talked about as top players during their professional careers but performed exceptionally well in their managerial careers. Interesting enough, there are players like Thierry Henry, Paul Scholes, Rooney, Gerrard and the likes of Lampard that we are talking about. Seasoned managers like Jose Mourinho never really played professionally as players yet he recorded great milestones during his active years.
So in essence, a good career will not be a guarantee if being a coach can bring success to the team you are managing and in fact that is how it is so far. The great coaches you mentioned have the capacity to win various titles with the brilliant tactics they have and I think we rarely see that today.
Meanwhile, the new young coach who went from being a club legend couldn't even apply his neat system when he became an active player and perhaps this is his individualistic ability that must be questioned. The EPL has always been a place of competition for great coaches and unfortunately we haven't seen that return and maybe Pep Guardiola will still be a coach who has no competitors for a while.
Pep Guardiola still has competitors because after all, Arteta also managed to make Arsenal have a good performance for at least the last two seasons. Although indeed, Liverpool and Chelsea have new coaches next season, but that does not mean Pep Guardiola will be easy to make Manchester City at the top of the table. Because of course, competition will still be able to occur, and there is nothing easy to maintain the position of the team at the top of the table throughout the season.
But indeed, about top players and failing when they become coaches it is clear, more top players who then fail when they become head coaches compared to top players and succeed also when they become coaches. Because it seems that, so far, maybe only Zidane and Xabi Alonso have really succeeded as players and coaches. But even so, at least there are still other names that have succeeded as players and coaches, even though their achievements are not as good as Zidane and Xabi Alonso but other names also manage to keep the team performing well like Xavi for example and maybe there are still other names that are not too exposed in the media.