You're mistaken.
> MacOS 9 [had] no preemption
Classic Mac OS has had vertical retrace (VBL) interrupts since System 1.0 (which are a form of preemption). But suppose we disregard that.
>> MacOS 9 had a preemptively scheduled kernel.
The GP is correct. Applications run cooperatively within the Blue task, but the Blue task itself runs preemptively with other MP tasks (which an application can create).
Very very little used it. About the only classic app I ever heard of that could even use pre-emption and background execution were some demanding Photoshop filters. Enough that Daystar Digital built multiprocessor Mac clones just for that alone:
https://lowendmac.com/1995/daystar-genesis-mp/
Within the MacOS kernel it is as coop as ever, and there were no different OSes inside virtual machines. No, Tenon MachTen does not count.