Korean Air Flight 801 could have used someone 2nd guessing a pilot. They didn't until they were almost dead and then it was too late. Not 2nd guessing the pilot was a really really bad idea.
ATC doesn’t have the kind of situational awareness or manpower to fix these kinds of problems the vast majority of the time. It only seems like they could have done something after the fact when the disaster has already happened and hindsight activates.
Like the GP said, ATC second guessing pilots is a really, really bad idea. A few incidents doesn’t change that.
...yeah, the second pilot. And in this case, also flight engineer.
IIRC The problem was pretty much aside from errors the cultural issues with pilots, the "lower ranks" wouldn't dare to be assertive to seniority and just voiced the issues they saw without doing anything.
Also, that sort of telemetry does exist for most major airlines, however it goes via satellite to the airline not the ATC.