If you take into account how un aero standard bike frames are - some have incredibly fat tubes which make the bike less aero than a 1960s / 1980s steel frame - then the savings of an aero frame are a must. I have seen a test where an old steel frame was compared to an aero frame in a wind tunnel, same wheels same position, and the aero frame was about a minute faster over 40k than the steel frame. Now think how a fat carbon non aero frame would be even slower than the thin steel frame.

I will try to find the link.

When you get to my age you realise that bike frames have been getting stiffer particularly around the bottom bracket by about 5% every year since about 1970. Those old steel bikes must have been incredibly floppy.

The tyre pressure and position on the bike is what you can feel on a bike more than anything else.