Or like CPU clock speeds, which have never correlated directly with performance across families, even when comparing something as old as the 6502 vs. Z80.
You get something that physically is very clearly defined but in practice it's not. Just like the minimum feature size which doesn't tell you much about the rest of the transistor. Perhaps if they used an average feature size it would make more sense for the regular person.
So how are the fabrication sizes different from the frequency that gets advertised on the box? "Oh that? It's only when you load one core. And don't run anything using these specific instructions. And when the temperature isn't too high. And...".