Valverde never won a Tour de France. When Armstrong started winning the Tour, he stopped participating in the Classics. The schedule of that Armstrong´s was more like Vingegaard's schedule than Pogacar's.
As I said, LeMond is the last rider who, having won the Tour the previous year, competed in Paris-Roubaix the following year. Thirty-four years have passed.
Only three riders have won a Tour de France and at least two Monuments in the same year: Meckx, Bobet, and Pogacar.
No, it's not common. You can't use Valverde as an example, since he wasn't expected to win the Tour de France, and despite being one of the longest-live cyclists in history, look how many times he's participated in Milan-San Remo and the Tour of Flanders.