This is true. The point is, even with the most advanced materials, designs etc, if you removed that part of a structure you'd have to compensate elsewhere. In a frameset without seat stays or radically dropped seatstays, you'd need to come up with some other way to introduce torsional rigidity so the rear wheel doesn't twist' independently from the front wheel. This is a consideration people often forget when they look at the two-triangle design of a bike frame.
https://www.cyclist.co.uk/in-depth/bike-frame-stiffness