It comes down to both sides being correct. I have no doubt that in the upper reaches of power and performance, separates are unequalled. Whether this is because nowone has tried to produce a "cost no object" integrated, or because the ultimate limitations of an integrated chassis, set a performance limit. None of us, I think, dispute the benefits of separating power amp transformers and heat, from the sensitive low voltage preamp stage.
The argument is better put, that in the world most of us live in, at the price we can afford, what gives you "bang for your bucks". To me the cost savings of a single chassis, make the integrated a serious proposition. This is particularly so, because manufacturers themselves are taking integrated amps seriously, with a number of very good units available now. Take Accuphase, krell, Mark Levinson, Music Fidelity in SS and VAC, ARC, Jadis, Viva, Unison Research, in tubes.
I have gone from separates to a tube integrated, the Viva Solista and get what I consider, serious performance at a real world price.