Concurrent mode seems to come out of actual research regarding managing what is rendered when and what people like / don't like and expect to be rendered and when ... and providing more control over that.
I guess that's complicated but I can see even basic apps benefiting from it.
In fact, most web applications only need this 200-line library: https://github.com/wisercoder/uibuilder
React started out as a simple library, but it is getting more and more complicated (see concurrent mode). 90% of applications don't benefit from React's complexity. This tiny lib has the same templating technology as React, but none of the complexity.