That’s not how it actually works. It sounds a little bit like you’re confounding hyper-threading (where one thread will execute while the other is stalled on missing the cache,) with (micro-)tasking code structure. They’re not really related.
In general, at the code design level, we build tasks that are big enough that a core stall is much smaller than the size of computation for each (micro-)task. This has been done in multi-core systems for a very long time (heck, I did it for BeOS in 1998) and is nothing new.
What is new-ish, is that game engines now must use tasking systems; a single thread is not enough to feed modern hungry graphics cards, much less the physical and particle and global illumination and audio simulations that go with them. Unreal has had a worker-thread / task-scheduling system for a long time, and one of the reasons to use Chaos instead of PhysX is that it’s allegedly better at tasking across more cores, so there’s some benefit to be had there.
For content creation, the longest tasks that benefit the most from multi-core, is lighting processing (“build” button) and shader compilation. Both of these have been multi-core all the way back to original UE4, so there’s nothing new needed there.