Ah, thank you. So, it seems that as these new regiments did not have the years of drilling to make them into totally efficient automata, as the older regiments were; that initially they were considered to be less efficient on the battlefield.
This is true of any new military combat unit; not specifically limited to `fusilier regiments` at any particular date
I can accept that - for a limited period only.
Combat attrition would have taken its toll on the older regiments as well. Their replacements would have diluted the regiments and slowed the rate of fire, reduced the steadiness etc.
As I recall, the Prussian army suffered fairly heavy casualties early on in the 7YW. A whole corps of veteran regiments was lost at Maxen and most of the prisoners died of disease, so didn`t return to service.
They would have to have been replaced by new recruits, maybe even Silesian dwarves.
This means, that after a year or two at most, the difference in the combat effectiveness of the old regiments and the new would largely have disappeared, as the old regiments lost that pristine edge and the new regiments gained in experience.