The marginal cost of renewables isn't zero, producing it causes more wear and tear than not producing it. Furthermore, if you pay negative prices as a result of a renewable surge, that might as well be considered into the marginal cost.

Even if the marginal cost was zero, you gave coal/nuclear as the cause for negative energy prices, even though they didn't exist before renewables came into the picture. You may claim that the situation is better with the renewables in the mix, but you can't claim that renewables aren't the ultimate cause of negative prices in this case.

Similarly, you may claim that coal/nuclear are slow/expensive to regulate, but then must also concede that wind/solar can't be regulated up at all and couldn't provide a stable supply without e.g. natural gas, or a buffering solution that currently doesn't exist (at scale) and isn't priced into wind/solar.