For the original F/10 system used for 35mm photography the coma correction was good for that application. Exposure times on 35mm film was many minutes so seeing , guiding issues and the swelling of the star image on film reduced the visibility of coma. So coma didn't need to be perfectly corrected but good for the size of 35mm frame but better then a design with a spherical secondary. Then people wanted to reduce exposure times so they designed the f 6.3 focal reducer. Which again was design for a 35mm frame.
As time went on CCD showed up. That greatly reduced exposure time so coma was now more of an issue. At the same time production cost went up and one of the major costs is the skilled manual labor to aspherize a surface. The "holy grail" in optical engineering is spherical surfaces since the production cost is less. So to reduce cost and also have a selling point both Meade and Celestron went with the "coma free designs". Now they are using spherical optics and to correct for coma and they added spherical lens to do that. The production cost is less for adding a couple of spherical lenses vs one hand figured aspheric surface.
So they reduce costs and have a selling point for astrophotography. One has to look at the design from both the optical stand point and the business stand point. You need to make a product that people want to buy and one that can make a profit. People are looking at this issue from just an optical stand point.
On the original Celestron design there is no advantage to having a spherical secondary if your going to have someone manually figure it to null the system out. It is a no longer spherical. The cost is the same if you design the system to aspherize the secondary to also reduce coma. It makes sense optically and also from the cost bases since the time required is same hence the cost to produce is the same.
Really interesting back and forth here. I have no dog in this fight, but I do have a simple question.
Why would Meade introduce the ACF line when they (and celestron, apparently) already correct for coma by figuring the secondary?
Inquiring minds (at least mine) want to know.
Peace to all,