I'm not sure what you're reference point is for 'new', but looks like it's still Expedia as the underlying vendor to me. That's been quite a while ago since that change was put in.

I had several flights in December and January on AA that I booked via the Chase portal and they all credited as special fares, so buy fare class and distance. I don't know if that's the norm or exception though, I posted about it in the special fares thread and no one at all replied. Overall it worked out a bit better for earnings but not by a gigantic margin since they weren't very cheap tickets. If your tickets are extremely cheap then obviously distance based earn is going to be better in most cases.

The only benefit to booking on AA.com would be changes before your departure date. If that's something you do frequently, the Expedia reps handling the Chase portal are fare more difficult to deal with as they aren't trained travel agents. They barely have the knowledge to do anything that doesn't appear on the web browser. But once AA has control of your ticket then it in theory would be the same for irrops handling.