Of course it does. Roundwounds are brighter and thus louder. Brightness and loudness are the keys to mixing. Since they are scientifically proven to be addicitive, a good engineer and musician or composer or conductor must learn to control the impulse for more loudness and brightness. Its not easy to do, it takes a lot of experience. Because the a/b test is a widely used, yet misguided tool of the engineer , musician and everyone else.
Ever hear of the pepsi challege of the 80s? Pepsi exploited a phenomenon of human psychology and perception. They realized that pepsi woild taste better than coke if given in small sips, because pepsi is sweeter. Thus people chose pepsi over coke. But when scientists actually did double blind tests with larger amounts, the advantage was negated.
So anything sweeter, or in this case louder or brighter are better in comparison, but not in the absolute. If you did blind tests of short samples of flats vs rounds, i bet rounds would win. But if you did entire mixes. It would be different.
Yes its a reality that all things equal, some people just prefer rounds, but i think the popularity of rounds over flats is due in large part to brightness and addiction to loudness.