(a) is primary. Problems in physics are much harder to solve than they were.
For instance, the thing that corresponds to general relativity today is quantum gravity. Other paths exist, but the two that are most traveled are string theory and loop quantum gravity. The math involved in either one is considerably heavier than Einstein's relatively theory, and neither one is in a place where you can calculate real observable things.
There's plenty of (b) to go around, but it's hard to believe we'd know what dark matter is, discover supersymmetry, or have an established "theory of everything" if we cleared away the cobwebs.