Heavy infantry Cassadores don’t make any sense, but the legacy units don’t need to be overly scared. Cassadores were a late development so I could see them becoming an age 4 unit like Bersagliere to make room for other light infantry. Either way, I’d rather they just get rid of the Ordinance Rifleman as it’s a totally redundant unit the way it is.
Streltsy are a good example of an original unit with the wrong tag. They were absolutely heavy infantry with their short ranged guns and huge battle axes. The actual Russian units that functioned like in game Streltsy are the Opolcheniye.