For the past 2.5 years. On top of the previous models, ditto for them.
My current 12-core 3.33 GHz workhorse went into “production” work way back in September 2010. Nothing in it impedes my work. It just gets the job done efficiently, every day. Well, if it were 2X faster that would be nice. Would I get more work done? Unlikely.
The key is that enough memory, a fast PCIe SSD, dual 30" wide gamut displays and disciplined redundant backup are where money should be spent for a workstation, whose CPU speed and cores should be chosen for the actual tasks. Outfitted properly, the thing will hum along nicely.
But the current Mac Pro is 'no good' because it’s not new.
Especially for larger jobs, the Mac Pro has no peer. Ditto for anyone whose data is valuable and needs redundancy and backup without a rat’s nest of cables.