The 737-NG is relatively safe. By hull-loss accidents per million departures, it's safer than the A320ceo, less safe than the A320neo. You're thinking of the 737 MAX.

Previous generations of the 737 are among the safest jetliners ever built. The MAX will eventually end up there, too - keep in mind that aviation disasters are increasingly less common as time goes on.

This issue (wearing on the trim jackscrew and hinges) is not one that you would expect to see for many, many years. It's the kind of issue that you see on jets approaching 30 years old, and it's really hard to predict how and when this kind of thing happens.