For some things I'd say "X was good and Y is as good or better" and for some things I'd say "X is just marking the time period" - for instance "Y is the best thing since sliced bread" would mostly (to me) suggest a time period whereas "this is the best weather since 1990" would suggest (to me) that the weather in 1990 was especially good and the weather now is comparably good, although it is possible it would suggest that the weather now is better than all weather since 1990 but still not actually *good* depending on, er, the weather.