Barca DNA means Depression n' Anxiety these days.
This is always going to be a case with certain managers who have previous histories with a club as a player.
No top club, other than Fc Barcelona, would hire a manager who has had as many failures of their resume as Koeman had. It just doesn't make any sense.
There are 3 options for the TOP CLUBS in football:
1) Hire the best managers in the world I.e. Pep, Klopp, Tuchel, Simeone
2) Hire a (young) new promising manager i.e. Pep (10 years ago at Barca) Lucho, Zidane, Nagellsmann, Ole, Kovac, Flick, Pirlo, Ten Haag, Pochettino - This is usually high risk/high reward and as seen can have big success or catastrophic failure.
3) Hire an experienced (Older) manager who has done well at lower to mid clubs and looks to be ready for the next step i.e. Valverde, Sarri, Pellegrini, Mancini, Conte etc...
These are the only 3 options and have been the models for success in football and Koeman fits into neither of these.
There was no rationale for hiring him. His CV shows it through had through.