That's only true if generations don't overlap in performance. If they do overlap, either the company "ports" the old products into the new lineup or you're in for considerable homework.
Do the two different generations have different TDP envelopes? I though the 5xxx and 4xxx series both use Vega - what is the appreciable product difference between Zen 2 and Zen 3 if the performance/TDP/graphics performance is the same?
the point is that it's annoying to compare 4000 series parts against 5000 series parts to figure out what is the best budget AMD CPU. outside of enthusiast circles, no one cares about being on the latest architecture. they care about what is currently the best performing part within their budget.