Just because it's deterministic doesn't mean it is clear at the outset. Yes, when a developer sees the results, those will be the same on any console. But they may find some workloads resulting in lower clocks and therefore lower performance, and may not know that until they try.
however - if Cerny's description is accurate this will be rare, and most workloads should run at full clocks.
so Warren's comments aren't necessarily inaccurate, but I do feel the 'variable clocks' are often posted as though they're more like regular PC clocks, which they aren't. It would be nice to see More balanced reporting on that, vs what often does appear to be more fear mongering