The first project is using tsc as the transpiler, which is becoming less common in new build setups. esbuild and babel can already transform TS to JS extremely

The first project is using tsc as the transpiler, which is becoming less common in new build setups. esbuild and babel can already transform TS to JS extremely quickly and with full flexibility, they just don't perform type checking—which could be performed in parallel or even in a completely separate CI pipeline.