It is typically worth trying on such theories for size, no matter what their defects.
It is hard to avoid noticing that last year’s finalists — Miami and the Lakers — both exited this year in the first round, and ignominiously. Injuries and fatigue were part of the reason why.
The teams that are doing best — Phoenix, New Jersey, and Atlanta — had minimal or zero playoff responsibilities last time around. Usually of course playoff performance is positively correlated from one year to the next.
We will see if this theory has predictive value moving forward. In any case, it does seem the league has discovered the margin where player fatigue truly is a binding variable.
Addendum: ESPN provides the data on injuries to stars.