I tend to agree that any US crew, who is actually flying a MAX today, should be able to deal with this.

But the public does not understand the nuanced distinction between foriegn and US pilot cultures and experience. Onviously public perception and confidence in the aviation system is important, so the grounding was probably the right thing to do. I heard a rumor the USG was looking at some information sources to rule out explosives/terrorism since there were rumors of that and some bizarre eyewitness reports. Apparently nothing found along those lines, so combined with Lionair, reasonable (not conclusive) suspicion that the plane has an issue.