Are integrated amps technically better than separates?

Is an integrated better or an improvement over separates?  Unequivocally no.  However, the more important factor that may be missed in this query is: Have you found a synergistic combination with an integrated that is very magical and satisfying?  That answer is apparently yes.  Should you go out and spend a large amount of money trying to improve upon what you currently have with separates (chasing after a small improvement)?    Probably not but that is your call.
 

Have 2 high quality systems. One has separates - 2 mono amps, preamp - that list for $20k.
Other has $7k integrated. Sound quality is about the same, although they sound different. However, the room sonic characteristics dominate the difference in SQ between the two systems.
For me, the integrated is obviously more cost effective.

Not a good thing to put your sensitive preamp circuitry in close proximity to the power supplies for both the preamp and power amp.

One of my  preamps has a separate power supply that is connected to the rest of the circuitry by  special umbilical line - they recommend separating the two by at least a shelf or two in a normal stereo rack.  The power supply also functions to provide power to other components.

Certainly an over the top approach, but that reflects thinking at that time on the topic.

https://www.youtube.com/watch?v=-cXCFfec5mI

The power amp it plugs into is also pretty extreme

https://www.youtube.com/watch?v=RE5nlQ9LPYY

In my Audire amps, with its two 500 watt transformers, 8 26,000 mf caps, multiple outputs and big heat sinks, there is no room for similar, but smaller preamp parts.  Not to mention (What a phrase!) the magnetic emanations that would require major shielding between the big amp parts and the preampe.g.  I am not enthralled by 1000 watts of transformers, and 208,000 mf of magnetic/electrical generating devices next to my moving coil preamp.  Why don't we just add a tuner, too. and a CD player, then carry it around on our shoulders?

I would like to share my PC experience, however, I will not mention the "high end/boutique" brands used.

The amps I use are Krell KAS dual chassis monoblocs.  These, have a built in volt meter on the bottom chassis, which show/read power coming in directly from the wall outlet. Changing/swapping out PCs has a direct effect on what the incoming volts are and thus what is illustrated on the built in meter.  Unless the amps are biased to any one PC, the volt reading changes in regards to the PC used...and so does the sound quality.

Best,
Jose