True! It sometimes drops even more, which definitely makes spot instances attractive. The r5.16xlarges had a ~80% discount and a <5% termination rate for while.

Also, if all of scientific computing switched to AWS in order to exploit spot instance pricing, I don't think those market dynamics would stay the same.

As an aside, I've had trouble created large clusters of high memory instances in us-east-2. They might have increased capacity recently, though.