Apples or Oranges
AIS is not using the same protocol as Packet ax.25. There is no two way communication no CRC error checking. I honestly I don't what protocol AIS uses but it is one way thus they likely use a FEC (Forward Error Check) that does not require two comms like CRC does. Also all of AIS is over water not land like APRS so propagation is defendant as well.
> AIS is not using the same protocol as Packet ax.25.
Correct. AX.25 is primitive and long in the tooth. In computing terms, it's a relic out of the Cro Magnon era.
> Also all of AIS is over water not land like APRS so propagation is defendant as well.
I'm plotting vessels with AIS that are on the other side of the Santa Cruz mountains, while I'm in a mountainous valley where even FM broadcast is barely receivable. I have an APRS receiver (Kenwood D710) with an identical antenna, at exactly the same height on the same mast that hasn't even comparatively 10% the range to APRS targets - some of which are blasting 50 watts. AIS is 25 watts for "Class A" and 2.5 watts for "Class B".
It's the protocol that's bad - not the propagation. We Hams should be able to do better.