This is a different story, it is not about raising second class troops by default classed as second class troops.
There Füsilier Regiments (and not the Saxons pressed into Prussian servie, most had to be disbandede anyway soon) were raised mainly form new provinces and Kantone, were in the avarage not as tall as the old regiments, had shortened muskets, they were sort of classed inferior by Frederick, for more in depth information read either Duffy's second edition of Frederich the Great'Army or speak to him himself.
Bleckwenn is echoing the assesment by Duffy or vice versa.