It’s more that you can run more orcas simultaneously than you can barges, and you can do so for hours without needing to press anything. It’s the afk-ability that miners prefer. That’s why mack/retties have always been more pupular since 2012.
If orcas are commonly being used in groups as straight mining vessels rather than supporting barges then there’s a problem IMO.
And no it’s not ganking. Skiffs/procs are definitely tough enough and ganking is not rampant.