PV is not heavily subsidized compared to other energy carriers, and the learning rate has been extremely consistent for a long time.
LCOE takes some of the system costs into account, but it's of course true.
And your second sentence is not how energy markets actually work. Of course I make a contract for reliable supply, but I don't contract with an individual power plant. I contract with an energy company and that buys from the cheapest supplier mix (aka merit order).
The long term contracts for base load run for years, but those, too will eventually have to adpat to the reality of abundant cheap daylight energy.
My main point with PV isn't about the system we have right now. It's that we are in the first days of a new system structured around the new technological reality that only recently emerged. Until very recently nobody, even the optimists, expected PV to get that cheap that fast. It will take decades for the repercussions of this phase transition to shake out. The issue is, due to climate change we don't have decades.
You can absolutely sell non-PV power during the day. Big power consumers sign contracts for predictable and reliable supply.