There are counter arguments to this. Clouds and wind are local weather patterns. We can use cables to move power around between areas with and without clouds. Moving power over large distances has gotten more feasible with high voltage direct current (HVDC) cables. There are a few projects in the works to move power from e.g. Australia to Singapore and Morocco to the UK. And there are already cables moving power between e.g. Canada and California, Norway and various countries in Europe, etc. More cables means more resilience in the grid. Continent wide absence of wind and solar generation is not a thing that happens a lot. Certainly not for weeks.
Another point here is that demand shaping is an effective way to deal with fluctuating supply of power. By creating financial incentives, you can get energy consumers to scale up or down their consumption of power. Night tariffs are still common in places with a lot of static generation, for example. With solar generation now being so common, we even get occasional negative energy rates in some places where the static generation can't be scaled down.
Batteries and cables are a key enabler for demand shaping. Also, the time windows that energy gets sold for are getting shorter. It used to be that you'd buy x amounts of mwh for some price for hours. It's now getting down to minutes. That means grids can respond more rapidly to fluctuations in supply and demand. And of course it creates incentives for companies to invest in being able to scale up or down their energy consumption from the grid and benefit from these price fluctuations. For example by having batteries and using their roofs for solar generation.
Base load is of course a very flimsy concept and the discussions about it tend to be very hand wavy and rarely cite specific numbers in GW needed. Because as soon as you do that, you can talk solutions: cables, storage, more solar (it always generates some power), etc. And cost.
Hysterical assertions that we need to spend double digit percentages of GDP on things like nuclear or fusion kind of fall over when you apply some rationality to that. How much power for how much $? Maybe do something less mad and cheaper instead. Build some cables. Add some off shore wind. Much cheaper, faster, and way less risky.
Of course the reality is that we still have plenty of base load for the foreseeable future. That's why the vast increases in wind and solar generation, which are now the dominant source of power in a growing number of places, isn't really causing any outages or rolling blackouts. Whatever amount of base load we need, apparently it's way less than we currently have because we have been removing lots of it from the grid.