Ignoring the waffle above me, and straight to the TS's question, there is relatively little that could be taken as proof that RET is wrong.
The structure of the earth has never been observed, our evidence for it comes from seismics and our best guess as to what would create the results we see. Of course, this is also backed up by things like magnetic fields, tectonics, and volcanoes, so it looks like we were right.
There are a couple of gravity anomalies, one in Siberia, which we only have theories as to why it happens. But, FE doesn't really explain that any better (and I can't remember the RE theory).
Thing is, RET is pretty damn good, no gaping holes anywhere. Well, nothing that sends people (well, geologists/geographers/environmental scientists) off debating the shape of the earth.