People who think the Lineal champion defending against unwarranted opponents is some new trend need to go out and do there homework. As for the Heavyweight lineal title, there is zero argument that it is still vacant. Wladimir vs. Povetkin was clearly #1 vs. #2... if you hadn't already recognized him from the Chagaev or Haye fights, which people have made legitimate arguments for (although Wlad vs. Haye for the lineal title does not vibe with me as Haye was always behind Povetkin).
That isn't the case for just lineal champions. That's the case for all fighters whose economic impact is of a "star" or "superstar" level. What you said applies to fighters from Pacquiao to Chavez Jr to Huck to Yamanaka. So what you are saying is that maybe lineal champions need to be held to higher standards? While I agree, this hasn't been the case throughout history so I see no reason for it to change. Money makes the world turn.