The pro offers a larger buffer/memory & fibre channel ports (I believe they offer 2 so both can be bonded to a single faster interface). Fibre channel is faster than GigE & therefore faster than USB3.
Presumably the file sizes are large enough to "warrant" such a connectivity interface technology that provides faster downloads - especially for the professional series, whereas amateur/consumer versions one can "wait" a little longer with USB3 interfaces.
I'm hoping to pick ZWO MM as that is significantly cheaper than the QHY. You're right that the total cost of the MM is going to be significantly more and I think it's going to be the filters themselves especially if going for the Astrodon or Chroma 3nm's. Are you sure of the QHYCFW3 being $1300? Even in Australian, compared to
CyclopsOptics QHYCFW3 is USD$630 only (AUD$930). Even in Australian taxes, etc. that's a significant AUD$370 overhead.
You raised a good point about the need of a hefty focuser. The ASI combo (camera/FW) is estimated to be 1.63kg without any interface adapters, filters in the FW, nor OAG. This shouldn't be a problem for my µ250CRS (where the focuser is the secondary, although imaging circle is only 40mm + vignette), nor 125SDP with its helicoid focuser (imaging circle of 88mm), however it'll probably be too much for my FSQ-85ED.