Teams like Leverkusen and Athletico Madrid come along and have a good season or two and then fade away, over the past few years instead of Leverkusen being up there it's been Schalke, Wolfsburg, Werder Bremen, Stuttgart and instead of Athletico it's been Valencia, Villarreal, Malaga and look at these clubs now. These clubs usually have a good long run because of , as in the case of Athletico, a great manager. When they lose Simeone they will fall back just like Valencia. These clubs in Germany and Spain have never had the staying power like Bayern, Dortmund, Barcelona or Real Madrid because these clubs are so much bigger than the rest.
As for the EPL I think you are being totally unfair on the other clubs to say its simply down to the big clubs being inconsistent. For me clubs like Arsenal, Liverpool, Newcastle, Everton, Spurs have slowly got stronger over the last 5 years to make it a more competitive league.