Someone already did look at 15’s, and while Ret wasn’t last it was in the bottom quarter of dps:
But you can look for yourself:
Keys for Ret:
Keys for MM:
The only time they are sort of close is the top 10 or so, otherwise there is a significant gap between MM and Ret. You can easily look at 20’s there as well and see that MM maintains a 2-3k advantage for nearly every key.
You can also look at other specs as well from those same links, just click on the class and switch to another spec. What you will find is the comparison made in the first link I posted here remains fairly valid across most keys. Ret is bottom quarter dps, as in 25% and below, but they are not last. So you can hang your hat on the fact that feral is objectively worse at dps than Ret…
That last bit was a little unfair, Ret should be a bit better than Feral, Demo, Enh, Sin, and Destro. Ret should be on par with Frost DK. Ret should be a bit worse than Unholy, Shadow, BM, Arcane, and Outlaw. And Ret is objectively worse than Balance, Survival, Sub, Fire, Arms, Affliction, Elemental, Havoc, MM, Fury, Frost, and WW.
But not everyone can be WW, I encourage you to take a peek at WW. WW is broken.