"Baseload" clearly exists. There is a minimum load on the grid that it never falls below, which can be satisfied by constant-output generation methods that aren't as well suited to varying output, but also don't vary output and so can't don't create a shortfall when low output periods in variable sources last for longer than the usual amount of time or coincide with high demand.

> The sum of a bunch of intermittent sources is sufficient.

That only works if the intermittent sources are independent. In winter, solar output is going to be lower during the day than in summer, zero at night, you will have more hours of night, and heating load is both higher in winter and higher at night. There aren't going to be panels on one solar farm where this is the case and others that produce more, it will be true for the entire hemisphere for the entire season.

You're then left relying on wind if you don't want to use nuclear, but wind costs more than solar, and now you're lacking independence again. Weather is regional. There will be days when it's still and cold across a thousand square miles. Even batteries that could hypothetically take the load for a night are not going to have anything left by the end of a week of that, so you either need baseload generation methods or some currently unproven/uneconomical ultra high capacity long-term storage system or the week when that happens the power will go out and people will freeze.