Whatever external processor works is great! Is it cool that you can create these same effects from the P12 delays? Absolutely. Would I rather have those 4 delays ready and waiting to modulate, mangle and create chaos in a P12 patch? You betcha
It's better to use external effects for reverb because the one you can create with the P12 often sounds metallic.
But for the chorus, very few effects units have an ensemble one, Nord wasn't crazy not featuring a chorus in the NL4 (they could have, the Nord Wave had a good one) and a fantastic chorus ensemble on the A1.
I also recently bought a Strymon Big Sky on tried it on the P12 and it was a pure trip