I'm not this is really an alternative, at least a direct alternative, to Jest. Jest is much larger - but you get a LOT more functionality, so this isn't really surprising. You don't just get a test runner, you can a fully fledged testing environment.

I haven't found Jest to be a bottleneck at all, but all the other stuff (transpiling TS, rendering a DOM for React component tests, etc...). Jest supports all this out of the box, more or less, or with a few plugins - baretest doesn't. I guess you have to configure external libraries (jsdom, webpack, babel?) to do this with baretest. Now your tests are slow, like in Jest! Turns out the test runner isn't the bottleneck, but all the other stuff that happens before the actual execution.

Some real benchmarks would make this article much more convincing - and not just with a basic "sum" function, but various examples (some simple node tests, some API tests, some jsdom tests...)

I don't think baretest or minimalist libraries are bad, but I also don't think anyone using Jest could really consider this an alternative, unless your use case is very simple.