This is all quite thought provoking. I can firmly see the logic of these arguments, and I have in mind a 'wear curve' which is like an exponential graph, and these 5 minute/takeoff ratings are on the inflection before things go off to very large numbers and shake to bits.
However there may be an argument whereby the Robbo is simply lower down on this curve behind the inflection. I do appreciate that we're not just talking about the engine here but it's possible there's a connection to the fact that the engine is so derated.
More in hope than expectation I've dropped RHC a note to ask if they are prepared to share their view on the matter. I'm not really expecting a black or white reply (or even a reply at all !) but if anything meaningful comes up I'll post the gist of it.