Are manufacturer AC cables good enough?

Those people agree with me 100%. They have decided vanilla and chocolate together is better than vanilla or chocolate. I agree with them. They agree with me.

Now would you like sprinkles or nuts?

Hey Glupson: on your ice cream analogy, those people have tried them both, have eaten both vanilla and chocolate ice cream, and they decided which one they like. I don’t think a vanilla ice cream lover never tried chocolate ice cream before deciding they like vanilla ice cream

Yes, I believe that thinking is flawed.  Most stock power cords are junk. MFG’s anticipate that you will be using a higher end power cord with their product. They don’t include a good one because it would increase the retail price of their product when compared to competing units that don't include a higher end power cord...which none do to my knowledge. 

Of course subjective listening and opinion is vital too, but equal measure of science is often overlooked.

There is a difference between "subjective listening " and "subjective measurements " the former can be dismissed the later is used along with "scientific measurements" in evaluating whether something has an actual effect.

If Ayre whose top line amplifier sells for around $35,000 tosses in junk power cords then I think I'll look elsewhere for a company that's tested all the parameters that can diminish the performance of their products. For that kind of money I expect a good power cord whose measurements equal or better anything put up against it.