Your workaround is exactly what he wants. He only needs a 3x3 panorama with the center straight down. A 25 photo 360° Pano certainly includes those images.So just do a 360 pano and delete the photos that are out of the frame you want or as as @Meta4 said just do it manually and know that more photos is better, try to get like 90% overlap and then you can’t miss.
As to why the pano function is different on the M2 and M1 I don’t know. I personally don’t remember it being about to auto pano with the center straight down but I could be wrong.
It appears that the Mavic Pro 3x3 pano algorithm center was based upon the starting orientation and elevation of the gimbal, rather than the current default of a horizontal elevation. Hence the issue.