One of the perennial questions, as respondents have already said, you get more bang for your bucks with an integrated. I went from a pre/power to a tube integrated amp, with the best sound I have had to date.
Traditionally the top of every amp line is a pre and mono blocks, perhaps that is just tradition. Some manufaturers, ASR and VAC come to mind, are producing integrated amps of real high end quality. I wonder if you said to CJ or ARC, money no object, make the best integrated you can, how close the result would be, to the standard Pre/monoblocks. I suspect they would not see a market for it, we are a traditional bunch and the conventional wisdom is, the very best sound comes from separates, so a high end integrated would not find a market with their customer base.
I know the arguments about separating power amp transformers from the Pre amp section and other advantages, but I wonder how much that is a justification for doing things the traditional way