Dave,
Honestly, I would agree that if the DCS App doesn't operate all Legacy engine functions, the percentage is still in the high 90's.
I should be clear, however, that Legacy control via the DCS App is restricted to Legacy engines and their lashups, and any other Lionel TMCC components, such as a TPC device or ERR module that can be operated as if it were a TMCC engine.
Devices such as the TMCC crane car (and, I would expect, the Legacy version as well) also work well from the DCS App.
The DCS Remote, however, can control only TMCC engines and Legacy engines in TMCC mode.