The only problem with your theory here is that MS13 can be easily tried in local courts.
MS13 are street thug crims requiring no special handling for optics and riot control purposes.
MS13 are scumbag illegals and the public knows it.
Try them in local courts and then send them back to mejico. No problems.
GITMO will be used for higher profile scumbags, whose arrest and trial may cause the inner cities and antifa assholes to destroy neighborhoods.
Just my 2 cents.