Usefulness usually means real world use. It took the theory of general relativity 70 years before we saw a real world application make use of it. The theory that led to modern hard drives (GMR) went from new fundamental physics in the late 80s to full commercial use within a decade. Things like the blue LED (1990s) or frequency combs (early 2000s) were even faster and can be found truly everywhere now (unlike GR). There are far more useful models out there than the high level overview stuff you might get from an intro to fundamental physics class. And even if you're into explaining the universe rather than improving day to day life, as I said, there's tons of stuff going on right now if you're in the right field.