The fact that TMCC locomotives run better under legacy is nothing new John, I've experienced the same thing with my 2005 TMCC mohawk. Legacy "cab1" mode emulates the old cab 1 operation. However, I'm under the impression you haven't run a TMCC loco in "TMCC mode" via legacy, difference is night and day.
From George Browns review in OGR run 228:" Legacy TMCC mode has expanded capabilities for much improved speed control of locomotives or power controllers that use 32 speed stepswhich includes all Lionel locomotives that have the original LCRU or the later modular ACDR,DCDR,or Odyssey motor driver boards"
"Without exception,every one of my TMCC engines accelerate and decelerate smoother with the Legacy system than they do using my original TMCC cab 1and base. And even better, several engines that are balky,or downright irksome,including my Lionel4-4-2 with one of the early attempts at Odyssey speed control,run great using the legacy system."
