SMB reproduction is before LMB reproduction in cooler waters and SMB eggs/fry are better at withstanding cool water temp changes. Thus the SMB have an initial feeding advantage in deep cool waters.

The TFS info is certainly possible as described. Local adaptation can also occur at the margin (a few degrees). Even in the south when a pond freezes over and TFS die-off , if the pond is deep a few can overwinter. GS is the usual replacement species in Northern waters (can get very ig however).