They're getting to the point where they're demand-limited rather than supply-limited - plowing through the backlog quite fast, and the GTO launch market is in a downturn.

SpaceX keeps rockets other customers "paid" for after they've landed (the customer pays for the flight, not the rocket). They've amassed a fleet they never had to pay a dime to construct.

I believe they have eight block 5 Falcon 9s that landed successfully. More if you count previous generations, but those likely won't be reused.

Does the price of a launch completely cover the cost of construction (excluding R&D)?

It does, for the competition, and there is no reason for SpaceX to go much lower as long as they don't build excessive overcapacity that needs to be filled.

Yes. They actually improved a lot of rocket construction and that's why they were cheaper then everybody else BEFORE re-usability. Now re-usability they just increase the profit.

Until somebody else challenges their price, they can get huge profit from every launch.

Not if the opportunity is to be ahead of your rivals to a new market frontier and guarantee a head start

Even then you're trading one opportunity cost for another.

So then make the competitor pay for it: each time they launch for a competitor, add a margin equating to the total cost of deploying a Starlink satellite.