I wouldn't base the quality of a stem separator based on the quality of just one instrument on one track.
Wise words...
I now have a 2nd datapoint.
I extracted my own bass line from my most recent composition
Down Periscope Several months ago, I originally recorded this bass in Studio One in ver 6.something, and I used a version of my mix that contained no compression. I consider this another tuba test because it contains low frequency submarine rumblings. It did incorrectly extract those rumbles but it also extracted my bass clearly enough to easily percieve the melody, tone and rhythm of my playing; including some timing flubs on my part

Of course anything is possible with AI models including hallucinations. But AI researchers are making big strides in solving the hallucination problem. The proof is always in the pudding and the pudding is saying PreSonus and their partners hit a home run and I'm expecting further improvements yet before ver 8 arrives.
If anyone is able to cause this stem separator to clearly fail, do share your results.
On a separate note, I was quite proud of myself in being able to capture in a 2 page, 16 step process how to create
tempo maps in S1 based on a Gregor YouTube . . . another solid piece of PreSonus software engineering in its own right. From what I can glean so far, this lengthy process has been reduced to a few mouse clicks in ver 7.