One major flaw in dpr and nova damage comparisons is assumptions. However, this can be mitigated by looking at various scenarios.
However, one thing that cannot be mitigated is the performance differences resulting in being able to respond to harder encounters with more damage and easier encounters with less. Essentially applying that damage where it’s needed. As an Example, Rogues falter here a lot as their dpr is extremely consistent.
All this said if I have one character consistently doing double the dpr of the others across multiple scenarios, there’s enough signal there to conclude he’s a much better damage dealer (as long as his accuracy isn’t too low). That said if a build is 10 or 15% higher dpr, that’s probably well within margin of error.