If you switch out some of the LEDs then I have to assume that the light output is still reduced by the number of the total system LEDs that are turned off versus the number that are on. I read some parts of the web site but missed the part with the LED switching circuits apparently.

I agree though that light outputs are frequently overstated and very few people can afford to invest in an accurate Lumens measurement test setup. The high intensity LEDs you mention require more current I believe than most dynamos can put out based on flashlight use specifications I have seen. With dynamos multiple headlights are typicallly run in series which increases the load resistance, raising the voltage output of the generator. As I recall the same technique is used in the multiple LED homebrew headlights.

I suspect that Peter White's statement about light output may be based more on beam shape than total light output. I know the IQ Cyo has a very sharp beam cutoff at the top while reading his comments on the Supernova HL3-D it apparently does not if I interpreted things correctly. When I was in Europe years ago I noted that their headlight beam shape for street legal car and motorcycle headlights had the same sharp cutoff characteristic, much sharper than on American headlights.