Are OTPs approaching custom standards?

Customs are made to fit into whatever clique you want to be accepted by.
FACT.

Bollocks, my Jackson was built for me not a clique

Question (and I'm being serious): are there any frame builders who will build you a frame to your EXACT specifications, based on your size? All the frame builders I've seen build frames using standardised tube lengths (i.e. 24" 24.5" etc). Is it actually possible to have a frame built using, say, Reynolds 631 tubing with a seat tube of 25.1" ?

Yes, of course.

Here's a question?

If someone is fitted for a custom-made bike, will that fitting be right for them 20 years later?

I've been lucky. The frame I had built for me when I was in my mid to late twenties, still (at the age of 47) feels better than any other bike I ride.

I'm not sure anyone is looking down on OTP riders, ...
All I'm saying is that if you choose to make a comparison between an OTP and a custom, then you must compare on the differences, and the differences are not the components ... the differences relate to the frame and the way in which it came about.

+1. While having my Jackson restored I rode a Fuji OTP. It was a perfectly adequate bike, but the difference I noticed when the BJ was finished was indescribable.