The geological relationships of the various formations are quite clear.
The lava flows which spill into the canyon must be younger than the canyon.
That data is lacking from Austin's published works.
The attempt to abuse the meaning of a single contrived date -- which was produced only by a sample selection geared to dating a different event, and only for samples whose results were known by Austin in advance -- says a lot more about the level of competence or honesty in this creation "science" research program, than it says about the validity of isochron dating methods.
Even if given credit for discovering this case (which he clearly doesn't deserve, as his use of Leeman's data proves), Austin has only managed to "call into question" a particular sampling technique.
Even young-earth creationists would agree with this relative sequencing of events.
They would argue for a much shorter absolute timescale than mainstream geologists would accept, but the relative sequence is agreed upon by all parties. Steven Austin, chairman of the Geology Department at the Institute for Creation Research, claimed (1992) that he had derived an isochron for the plateau flows, which indicates an age of about 1.3 billion years.
In fact, the resulting age in this case may well be meaningful and accurate.