The Catalans may have been usurped as Spanish and European champions but their former defender believes that they reached unprecedented heights under Pep Guardiola
The Catalans lost their Liga crown to Real Madrid last season, while their bid to become the first side to claim back-to-back Champions League titles was ended in the semi-finals by eventual winners Chelsea.
However, Koeman still believes that what the Catalans achieved during former boss Pep Guardiola's four years in charge - a total of 14 trophies - and the way in which they achieved it, sets them apart.
"At this moment, Barcelona are perfection," the Dutchman defender told Canal +. "The best team in history."
Meanwhile, Koeman is currently preoccupied with getting his Feyenoord side ready for the new season, with next month's Champions League qualifiers approaching.
The Rotterdam club will enter in the third round and their 49-year-old coach is desperate for last year's Eredivisie runners-up to make the play-off stages at the very least.
"It helps that the group is in excellent physical condition, almost everyone is fit and the new boys are adapting quickly within the team," Koeman told his club's official website.
"It will be tough, but we are working towards being ready for the matches. It is very important for the club to get through our first round, so we are assured of the Europa League at least.
"But we will be going for the maximum and this is a challenge we will relish. I sense within the group the hunger for more success and I think that's very positive to see.
"Everyone is very keen to start the new season."
Koeman, who scored the goal that won Barcelona their first European Cup, against Sampdoria in 1992, took charge of Feyenoord last summer, succeeding Mario Been at the helm.