I don't know what you mean by "the performance question". A web component uses the same DOM APIs that React/etc. uses so it can have performance as good or better depending on how it is written.
The problem is coordinating rendering between components. React and similar frameworks optimise performance by batching DOM updates in one big read-compute-write cycle. With web components that don't share centralised DOM manipulation code its hard to see how that would work, and this can be a big performance problem.
