The points you have raised would be valid if the plants weren't here
They are not there, that's the problem, the current power plants are good enough to supply the current demand with some surplus, it's not just a switch button that would make power magically appear from some stand-by power plants, you might want to have a look at the list of all power plants in Texas
here.
Just as Phil said, the plants are there, they're just waiting for perfect conditions and contracts to be brought online.
For example, the exact list you linked to gives you 65855 MW capacity just for gas, and 18319 MW for coal, plus there are thousands of MW in decommissioned plants that can be simply bought by someone who has enough money and produces energy just for their needs.
You have 84GW just from fully operational ready-to-fire coal and gas plants, 5GW nuclear and whatever the rest biomass/hydro/solar/wind and those are the ones ERCOT has allowed to inject electricity.
And miners don't go for this, they go after decommissioned powerplants, like Harding , which Mrathon bought:
The Hardin generating station, a 115-megawatt coal plant located a dozen miles from the historic site of the famous battle of Little Big Horn in southern Montana, was slated for closure in 2018 due to a lack of customers only to somehow limp on, operating on just 46 days in 2020. “We were just waiting for this thing to die,” said Anne Hedges, co-director of the Montana Environmental Information Center. “They were struggling and looking to close. It was on the brink. And then this cryptocurrency company came along.”
Or Greenridge:
Greenidge Generation is a gas-fired power plant that previously only operated to provide power to New York’s grid in times of peak demand. Now, it burns fracked gas 24/7/365 to mine Bitcoin.
Or Merom:
Indiana's Merom Generating Station, along the state's western border, is a 40-year-old coal-fired plant. Its retirement was announced in 2020, with the plant slated to go offline in 2023. Then in 2022, that course was reversed. The utility that owned Merom sold the plant to a coal company to continue operating. In the meantime, a cryptomining company announced it was coming to town and would need a lot of power.
I know you're just like me used to a different system, with far fewer independent players in the energy sector, fewer price fluctuations and stuff, but things are different in the US, and on a different scale.
And.......we just went up 10% in difficulty and down to 63k in price, so that would be 4.4 cents???