Pogacar has 9 monument wins, MvdP has 8. However, Lombardia is certainly the least prestigious monument, 4 of Pogacar’s wins are in Lombardia, while 3 of MvdPs wins are in Roubaix, which is the most prestigious. So that evens out. Still Pogacar has more wins in the only other six classics that I consider significant (Strade, E3, Gent, Amstel, Fleche and San Sebastian), so he pulls ahead.
Looking at potential, Pogacar can win San Remo and Roubaix, at least if MvdP isn’t there. MvdP can win Liege if he makes it a more primary target, if Pogacar isn’t there, and if Alpecin shows up with a stronger team. Winning Lombardia seems impossible for MvdP.
So probably Pogacar as of now.
Remco isn’t even close. Especially not if championships don’t count. He may even be below Wout, who besides San Remo has won E3 (twice), Gent, Strade and Amstel and podiumed 4 diffenret monuments.