If there was an inherent issue with tyre longevity on Mustangs then it would be obvious.
You wouldn't have to cherry pick only a couple or few races out of all races to try to make a point; and you wouldn't have to talk about the speed of SVG and sometimes Chaz to try to make a point - not withstanding variables such as passing or traffic, you'd be able to show on Natsoft how every Mustang loses time relative to every Commodore in the later stages of every race at every event (or after a certain number of laps).
Of course that is over-simplifying - does not take into account things like different set-ups, different driving styles, different strategies, driving to a number early in a stint in interests of tyre preservation, clean air, and all the other factors that are being ignored which could also explain why one or two drivers/teams are besting one or two other drivers/teams - sometimes