Increased bulk, though still not that bulky, lets it live an unboosted move if it fails to KO the opponent. Its low Speed is also somewhat mitigated by a strong STAB priority in Sucker Punch. Dark typing also means that it isn't hard-walled by bulky Ghosts.But what can this thing do with this below average attack stat? Besides with his secondary stat, it doesn't even hit harder than regular Raticate and that thing is meh in PU. Even its bulk isn't decent and its speed is just below average.
Why would anyone run this?
Alolan Raticate is unviable in OU but that doesn't mean we can conclude that it is unviable in the PU just by theorymonning. It could end up being unviable in PU or it could surprise us the same way Alolan Marowak did in OU. All of these will come in practice after the tiers are completed.