I agree with ya to some extent. Quality of the players is one thing, another is how they are playing and gelling together. Take France for example, they have real quality in the squad but they clearly aren't playing well. So ya can't just see what teams have the most quality on paper, ya have to look at their form.
Obviously the intensity isn't quite the same as competitive games but coming up to the World Cup managers won't be experimenting as much. They will pretty much be playing the team that will play in the World Cup.
Also friendlies where both teams are going the the World Cup will be somewhat more reliable as an indicator than ones where only team is going.