Better error messages, an error-recoverable parser, faster speed, consolidation into a single tool, additional ability to lint/pretty-print/minify/test instead

Better error messages, an error-recoverable parser, faster speed, consolidation into a single tool, additional ability to lint/pretty-print/minify/test instead of just transpiling and bundling, having zero dependencies, having a smaller codebase. Maybe those things are not important for you, but they are for the Rome author and for many people in the community. Also with brundolf's solution you can run the TSC typechecker (but not the transpiler/emitter) and Rome in parallel, making good use of modern multi-core processors. With Webpack+TSC you'll have to typecheck, transpile and bundle all in series. This might be very significant.