No. It's complicated.
PZEV means the vehicle is certified by the state of California, and by selling PZEV-rated vehicles Subaru builds up pollution credits (ZEV credits) so to speak to allow them to continue to sell vehicles in CA--or they can sell their ZEV credits to other automakers.
So the PZEV is more efficient (cleaner) than the 3.6R, which apparently cannot be made quite that extremely clean.
So if you buy a PZEV subaru gets most of the benefit but you get a 150000 mile or 15 year emissions warranty (in those states that require PZEV)...and...I think 5 more HP or so.
Other states are adopting the CA designation.