I was actually reviewing decontam in a real dataset. I have actually observed your skepticism over time!!!!!
Many believe quite rightly that dominance or "prevalence" of an OTU is evidence to remove. The dataset I was reviewing just highlighted for me if the prevalence cutoff should be somehow decided per data.
So in the case for decontam, i have seen 8% prevalence of an OTU in blank versus 3% in actual samples gets that OTU removed (p is below 0.1). Yet if the OTU were cross talking, then its a real one and lost. Probably of interest in some kind of data