The sounds of the RT pianos is, in fact, sometimes the issue.
Especially the earlier RTs.
There is sometimes a "wash" of reverb-i-nessthat does not work in some mixes.
The solution to that is to use the MIDI Supertrack instead (most pianos have them).
You get the same performance, but can use whatever piano vst works for you. Easier to fit-in-the-mix.

150+ Songs produced using BIAB RealTracks
And 50 more...
and some more...