Well, it seems other reputable tuners do agree with me that making more power will use more fuel. I did a 300 bhp Sierra 4x4 set for Green Ligth Tuning from Gerard Sauer and was allowed to use 25% more fuel.

After a bit of struggling with the fuel usage I decided to take a look at the software for the L8 and found the bugs why it was using so much. Changed the software and got a perfectly good running car.

Gerard Sauer is not the man to take just your word, so he went to the Millbrook Proving Grounds with a completely standard car and the one with my chip (and injectors and 3-bar map sensor) in it.
He couldn't believe the measurement he got and rerun his test twice.
And that included a couple of laps at top speeds on the high speed oval.
The result was 23.6 mpg for the standard car and 24.1 mpg for the 300 bhp set.
So it all depends on the software and whether or not there are bugs in it.

I still do not agree with what you say about fuel maps and making boost.
Even the smallest turbo you can find will not make boost when you do not press the accelerator. So, also a T3 will not make boost unless you press the accelerator enough.

But hey, I am only in the (chip) tuning business for 25 years now, so what do I know about it.