It's hard to know for sure, because we don't have access to the PIO's implementation, but I suspect that the PIO is "not small".
That being said - size isn't everything. At these small geometries you have gates to burn, and having access to multiple shifts in a single cycle really do help in a range of serialization tasks.
That being said - size isn't everything. At these small geometries you have gates to burn, and having access to multiple shifts in a single cycle really do help in a range of serialization tasks.