When you buy a Swiss army knife your expectation is greater functionality and utility in a single package - it is not that you believe you now have the world's best screwdriver, knife or saw blade. The miracle of a Swiss army knife is how much they can pack into a single package not how good any one piece of it is.
In the same sense, when a manufacturer builds a preamp or integrated amplifier that includes a multitude of non-essential features it is more than likely what you will get is "good enough" for the task, not spectacular in its own right.
That's the thing with separates - they must stand on their own. If I build a separate DAC for $1,000, it had better be as good or better than every other separate $1,000 DAC or it will fail. If I include a pretty good DAC in a $1,000 integrated it is not expected to compete with the standalone crowd.
This is the paradigm of separates vs. integrated solutions. But it doesn't have to be that way. Most of these "truths" are simply marketing driven and technically they need not exist.
Years ago automobiles came with courtesy radios built in - you wouldn't buy a car without a radio, yet the radio's performance didn't matter because they all sort of sucked. Then an entire industry came into fashion building separates for the aftermarket automobile sound systems to fix this issue. Those separates were better than what the auto makers were giving you. But then the auto makers decided to up their game and integrate better stereos into their cars and charge you for them at the time you bought the car.
Today a premium sound system that's integrated into the car is almost always better than what you can purchase as separates and the aftermarket separates industry barely exists anymore. Why? Because manufacturers are finally taking advantage of the benefits of integration - actually designing the interior of the car with a sound system in mind. When you use integration to your advantage you'll always benefit over a collection of separate pieces cobbled together to form a whole.
What would happen if high-end audio manufacturers starting taking advantage of the benefits integration offers in their products and comparing the results to separates?