Are manufacturer AC cables good enough?

This argument is more akin to the kid who buys a $7,500 car, spends $12,500 souping it up such that it will blow the doors off pretty much anything off the lot under $125k in a straight line, but the person who spent $120k on their car still insists it is faster and brings up all kinds of stuff about aerodynamics, carbon fibre construction, valves per cylinder, variable valve timing, computer optimized air induction, and a whole host of other technical advantages .... Everything but test results to show their car is faster.

When you buy a TV do you ask for test results? Cause if you do that would be pretty dumb. Do you demand blind tests for TVs? No. Because that would be pretty dumb too.

No, I look at test reports for televisions. Many of them exist. They look at things like color accuracy, black level, whole screen and area dynamic range, motion compensation, screen ambient light rejection, etc. These are all things that are very hard to determine at your local Best Buy. That narrows it down to a couple models or, even fewer. Considering TVs at shops are never setup properly it’s almost meaningless to review them there. That is not what you do do you? Is your TV still on cartoon mode of the box? How sad for you.

that's the great thing about AC cables (or any cables), it's so easy to have them shipped, test them in your own system, double blind of course, and ship them back if you don't like them...much harder to do with a TV...

Yes but video runs on NTSC: Never Twice the Same Color.