Wawrinka has won 1 major, sure. But he is no spring chicken as he will be 29 next month. This year's 28 yr old Nadal, and 27 yr olds Djokovic, and Murray will eventually decline and they are probably approaching that point within the next 2-3 years. The average age of the tour is quite old right now, older than in over 40 years. Many will drop like flies in the next couple of years.
I imagine it will be near that point when we have some younger players in the transition winning, like a Dimitrov, or Janowicz, or Pospisil, or if Del Potro can get healthy, or Tomic straightens himself out, or who knows who. But then I finally think a great younger player or two will come along to overhaul them and dominate everyone. That's what one would expect historically speaking. But it might be 5 or more years before that happens.
Respectfully,
masterclass