I avoided dealing with moving weight from derailleur to frame because I agree. Apparently we both understand the effects of mass and its location.

My "thesis" was that generally more expensive components are better - and you generally get value for $500 - in that mid-range. I buy lots of stuff that is more expensive, lighter and "not better", but I am not like the OP. In the mid-range Ultegra and the parts that come with it are better than 105 and parts that come with it - that's all.

The 2nd point was depending on riding style/type - a rider may feel this difference. A 10,000mile/year rider would more times than not be able to tell you which bike was the $500 more costly.

I have put numbers to this stuff in the past (general physics in the 80s when I commuted to school by bike) and it is hard. I find tests matter more than calculations because no calculation I read account for the side to side movements and those vary a whole bunch rider to rider. I support my kid who is a 10K mile/year guy and I know he notices this stuff. Our recent and ongoing test - wheel weight and aero (see 33 Tech forum).