If base load were to drop due to crypto miners being turned off, the energy with highest marginal cost would be turned off, which means fossil fuels, not renewables.
The fungibility argument doesn't work when you consider that not all power generation in the world is connected to the same grid. There are crypto operations that use their own renewable power infrastructure. That energy never would have made it to the grid because there was no incentive for it to be put there (otherwise it would already have been there). The incentive is to use it for crypto not your mom's blender.