The OP's original question was written with too much hyperbole to be taken as a serious premise but if one looked at it more realistically, the case could be made that an decent mid-range bike would give as good or even better a work out as a very expensive racing oriented bike. That would be a better comparison to argue as it has real life implications in the way many people, who purportedly get into cycling for the exercise benefit, buy bikes far beyond the stated goal of exercise (buying bikes designed for racing instead).
In some ways a very light race oriented bike does subjugate the exercise goal as they are designed to go faster and cover more distance with less effort and many people do not ride them at the intensity required to equal the wattage output of riding a more reasonably priced bike.
Also consider riders of fixed gear or single speed bikes. Besides aesthetic/social and other considerations, an increased workout in comparison is one stated benefit of "underbiking".
That premise could be argued in a more realistic way.
Last edited by Happy Feet; 05-06-21 at 09:00 AM.