Is this opinion on personal computer flight simulators too strict or is it actually true? A couple of days ago I had a discussion with a commercial pilot and his opinion on personal computer flight simulators were a bit surprising to me. 

He said that flight simulators, even with expensive payware aircraft are about as close to the real plane as Call of Duty to real warfare.

He said that most of the time the systems and the switches appear to look similar but key factors when operating those systems are missing, mainly because the manufacturer keeps those details more or less undisclosed. The developers don't even know what to simulate and it makes every single flight simulator just a simple game that bares a slight resemblance to reality but that's about it.

This surprised me to say the least, because I thought the well known, premium payware planes simulate the instruments and the systems very well and all the details regarding those systems are available in manuals that we can easily find online.

But I didn't really know that pilot well so I just accepted his answer, I didn't want to seem rude and try to debate him, but I'm very curious if he told the truth or he just tried to exaggerate. I'm especially skeptic about his comment on the undisclosed nature of flight systems.
It isn't true, not as an indictment of the simulator software community as a whole anyway. It may be that your pilot friend doesn't have experience with modern simulators, let's take X-Plane for example...

X-Plane has a "professional use" version, which is simply the regular X-Plane with a commercial license and a few extra features. The underlying software is still the same. X-Plane "for professional use" can be FAA certified as a training device. 

This means that the aircraft behaves exactly as would be found in the real world. In fact, X-Plane is sometimes used to verify flight models before more expensive methods are used, and they are relatively accurate. NASA has even written research tools to utilize X-Plane. X-Plane's Garmin G-1000 is incredibly realistic, and X-Plane "for professional use" can drive G-1000 simulator devices. 

You can buy other "professional level" simulators for home use like the Redbird Jay which runs the same FAA approved software as the certified simulators. The same is true with Elite Simulator.