Fair point. In that sense I would say the question is maybe not esbuild specific but rather why using a bundler (webpack, rollup, esbuild etc.) and not just tsc?

In comparison to just tsc, I think it is worth to use a bundler to output specific bundles (ES6 for web or CJS for node), tree shake and eliminate unused codes, generate source map and minify the code.

Between all bundlers, esbuild is one of the fastest but, you are right, there is that gotcha that tsc is still needed if you want to output the typescript declaration at the moment.

Maybe summed together build with esbuild plus typescript declaration might be slower than than another bundler. That would be something to compare and analyze. Honestly I would not be surprised if still faster. Maybe that’s a good idea for another blog post 😉.