> such a build graph

Nonsense. All build systems implement a DAG of build targets.

> why caching tools can't be used effectively

Nonsense. There are a myriad of caching tools freely available, from ccache, sccache, build cache, etc. To get them to work, all you need to do is pass compiler launchers to them, which means setting a single env/build flag.

The author is either trying hard to make a mountain out of irrelevant molehills, or is outright being disingenuous.

Bazel is being sold as a solution desperately grasping at straw-like problems, while being feature incomplete.