The USRA Mikado seems to have been a good loco. so it is confusing as to why PRR didn't keep more of them. However they did have the large fleet of their own design and they had built a bunch of I1 Decapods for drag freights starting in 1916 I think. So maybe they just did not need the USRA version.
I think the 5 L2s were assigned to the LIttle Miami which was part of the Grand Rapids and Indiana.