Oh, I agree with you. I have brushed off dozens upon dozens of distros, because they just do not offer anything over Arch linux that I have always been using. Until NixOS entered my radar, that is. NixOS has many very unique strengths that you just can not get anywhere else. Due to that, it was the first to make me question whether I should make a switch to it or not.
However, I disagree that a “ton of knowledge” transfers. Putting aside the programs one uses, the way you set up, configure and maintain your system will wildly vary from a standard distribution. Which will not help you at all in case you want put all what you have learnt into another machine that requires said ‘normal’ distribution. But again, I understand that this is the whole point of its design in the first place.