I'd find ZZ to be much faster than petrus becuz even though petrus has fewer moves to solve whole F2L, ZZ influences last layer with EO and can be done with one whole alg with ZBLL. Just doing OLL and PLL on petrus could be fine, but ZZ has so many tricks up its sleeves that its just super efficient to solve. It may seem like petrus can just finish F2L faster than ZZ, but becuz ZZ has way much better fingertricks, ZZF2L is faster. And geez, if a ZZ user cant do ZBLL, that user can do phasing and then ZZLL which is just solving the whole last layer with only 170 something algs, or just use OLS->PLL or COLL->EPLL. There's so much flexibility with ZZ and I really think petrus doesn't really have much but just more freedom. The only downside about ZZ is that it is super difficult (and I mean VERY DIFFICULT) to get fast with becuz theres so much an average human can comprehend. You'd have to be very committed to become sub-8 or sub-7 with ZZ and experience/practice all the tricks to perfect your solutions and strategies.
