Your point about performance is well-taken and I agree. But there's the "custom-built-for-me" or "piece-of-art" part that I've come to accept are legitimate considerations too.

In my case it's a little of each of them. Riding with a disability, a standard bike setup feels clumsy and sometimes unsafe to ride. I want a nice bike that performs well; even fully equipped with function as the goal, that bike would only cost $3500-$4000 USD, new. The bike I'm planning is going to cost about $6000. Being completely honest, the rest is (for me) aesthetics, longevity of parts, and optimization of measurements, etc. For me the extra $2k is worth it to get "my bike" rather than "a bike."

A related part of this is an experiment, too. I've never had something expertly made just for me, let alone a bike. I figure if I spend $6,000 now, I get the benefit of a good (potentially great) bike, and I get to learn for myself whether all the hype and cost are worth it. If they are, then I have made a good purchase; if they're not, then I've still made a good purchase because, as someone on the forum said recently, $2000 is a cheap lesson to learn. And at the least I'll come out knowing that I never have to do that again.