RUH is harder to transit through (and also harder to get visas for) than AMM.

While the online tool tickets based on first airline, you could ticket through a TA or directly with another airline as long as they have some flights (some require longhaul flights) on the ticket.

The LHR stopover is costing you a lot in taxes, although at least it is at the end of the itinerary and not at the beginning (taxes for LHR-SYD are higher than LHR-MCT/AMM).

Changing JFK-YVR-DFW to JFK-SEA-DFW will save on taxes and earn more SCs (as JFK-SEA books into first).