Only in your mind. I am not knocking your preference, but don't incorrectly inform others that they are getting some huge advantage with a spherical lens. The fact is that they are not. An unnoticeable difference in aberration and an few degrees more on their FOV (field of view), depending on which frame they buy.
Well, I've already made my comment as to spherical being preference by stating that a flat lens isn't going to kill you (again, on a normal trail, can't speak for backcountry). And you were right about the anti-fog thing. Sorry. I thought I read on one of the company's catalogs that the tech was different. Looking through it again, it a difference between the years and not the current lines.
But, I still stand firmly on getting spherical goggles for many other reasons. You will get a better designed goggle. One other thing to note. Flat lenses are just fine, but there is a reason why you don't see goggles with a large coverage with flat lenses. Like an Electric EG 1 with flat lens. When you have that much lens coverage, spherical makes a factual difference. Top down vision would be distorted with a flat lens. With a flat lens, light travels through the top and bottom of the lens differently than when it travels through the center of it. This causes distortions which is why flat lens goggles have less coverage.
Edit: forgot to mention the top down thing with flat lenses is due to cylindrical lenses being tapered from only the center to the sides. Spherical lenses are tapered from the center to the top, bottom, sides, diagonal, etc...
Spherical goggles = more field of vision because of a larger lens coverage area, better designed frames, more technology on the actual lens i.e. Smith Vaporator (Regulator and Airflow do not have this)
All of those mentioned are huge advantages to me. I love goggles that minimize obstruction of vision and I have gone through many flat lens goggles and they all intruded in on my vision due to the smaller coverage area of the lens. That's just me though. Maybe seeing the plastic of the frame in all of your peripherals doesn't bother you.