I agree with someone above who said you need to compare the amps within the same brand for this to make any sense. In my opinion, a $10k integrated amp would probably sound better than a $5k amp and $5k preamp, assuming they were all the same brand. The big caveat is if you play vinyl… the included phono stage on an integrated is likely not as good as one included in a preamp, although it’s possible, I suppose.
There are way too many variables if you compare across brands.