And Baber conceded Cardiff had little response to an emphatic display from the cup holders at the Aviva Stadium.
He said: "Leinster are a smart and physical side who were better at creating and managing pressure. At half-time we wanted to restore some pride but in the end we were out-classed."
Cardiff were hit by a string of injuries ahead of this tie, including the loss of Jamie Roberts and Sam Warburton, and the weaknesses told.
Leigh Halfpenny handed them a second-minute lead but Leinster struck back through Rob Kearney, twice, Isa Nacewa and Brian O'Driscoll as well as 14 points from the boot of Jonathan
Captain Xavier Rush said: "Reaching the last eight in Europe is an achievement in itself but we wanted to impose ourselves more than we did. We were beaten by a better team, there's no other way around it.
"We couldn't get any rhythm to our game in the first half. Leinster put us under a lot of pressure and we couldn't put any back."