I will give credit to Souness as he was a successful manager when he started at Rangers. Back in the eigthies there wasn't much between Aberdeen, Celtic and Rangers but Souness made Rangers into the dominant team.
Of course it helped that when he joined Rangers, Alex Ferguson was leaving Aberdeen but he set the club up for all the success that Walter Smith had with them in the 90's and his time their was a tremendous success.
He also went to Turkey and won a Cup and he was decent at Blackburn for a while, got them back in the top-flight and won a League Cup.
Robson has done a lot less though. Saved West Brom from relegation and get Boro promoted and that is about it. For him too his best years were when he just started as a player manager. It seems that once the lustre of former legendary player wears off these guys tend to struggle a bit. Keane better watch out.