They have wijnaldum, Herrera and Danilo as well. All have legs to get about. Veratti is a passer rather than a destroyer in midfield.
Normally teams double up on Neymar and Mbappe. To use your example, how long would West Ham survive having to double up on Messi, Neymar, Mbappe? Then not seeing the ball for long periods of time while PSG just pass it around. They can overload the flanks with Bernat and Hakimi. If it still isnt going their way they can bring on Di Maria, Icardi, Draxler etc.
Get a chance to advance on the PSG goal, you got to then get through Ramos and Marquinhos and then beat Donnarumma. Unless you score or the ball goes out of play your open for the transition up to Messi, Neymar and Mbappe. So with that in mind how many players do you commit to your attack? Or do you park the bus and hope to get lucky on the break?
Regardless its not going to be easy. Messi, Hakimi, Ramos, Wijnaldum and Donnarumma have taken the first team up a level. They will be tough to beat. Oh if you cath them on a day when Neymar, Mbappe and Messi all have 9 out 10 performances, then your really screwed.