Real Madrid has been the most consistent club so far in both the domestic league and in international competition, indeed they don't always win every season but they have never experienced a dark period where their achievements have slumped as experienced by other clubs including their competitors in Laliga Barcelona which due to mismanagement experienced a financial downturn that resulted in them not being so impressive.
La Liga is a farmer league, the top 1,2, and 3 always Barcelona, Real Madrid and Atletico Madrid, they just swipe their position and there's no club can compete against them. I think the reason why Real Madrid is successful in international competition is their key players are still playing, it's not like Barcelona where most of their players were retired and they need to make a regeneration.
With Casemiro leaving and followed by Benzema, Real Madrid will make some regeneration. The big change happen when both Kroos and Modric performance aren't good enough, Real Madrid might have a bad season like Barcelona in the last year.