Not sure if I understand you correctly here. With "the coupling ... is just too strong to ignore" you mean that if someone has one of the subclasses at hand, th

Not sure if I understand you correctly here. With "the coupling ... is just too strong to ignore" you mean that if someone has one of the subclasses at hand, they should automatically have all the extension methods at hand not having to look for them somewhere? > Your example with the counting stack made use of "super", which is always a red flag to me. "super" is such a bad smell to me, that I literally never use it. I think that's a sign that you have developed a good intuition of that it can lead to problems! :)