I do agree with you with the measuring aspect. Part of building high-performance systems is being able to measure performance in an accurate and actionable way,

I do agree with you with the measuring aspect. Part of building high-performance systems is being able to measure performance in an accurate and actionable way, and consequently optimise code paths that have significant performance impacts. However, I do believe that a competent engineer would have the judgement to be able to see, roughly, where performance hits would likely arise and optimise accordingly. Command-line arguments would likely not fall under this mandate, but serialisation to stdout is likely a good candidate for well-designed and well-optimised code. A nice side-effect is that this also avoids significant refactors down the line when you need to, in this case, change your serialisation from dynamic dispatch to static dispatch.