To continue dissecting this, since I don't have anything better to do right now:

What you do in that time depends. If you drive a faster car, sure, you'll travel a further distance in less time than a slower car. If you use the same car however, the distance is as meaningful as the time for a symbol of progress. Since technological and scientific advancements in general don't depend on people driving around in cars, but on people investing a lot of time and effort, I would prefer time as a measurement.

Usually, if we think about scientific, technological or cultural progress, we tend to judge based on time and not on distance. For example, consider some indigenous cultures which live their lifes isolated from the rest of the world. They are often compared to primitive "stoneage"-like cultures. We specifically use time as a measure.

However, I am not completely opposed to agreeing with you. I think it depends on what you want to emphasize. A distance can be useful for reflecting some aspects in which, e.g., a software, takes the lead compared to alternatives. Then again, time would be better suited to highlight very innovative features or significant futuristic advancements which may have groundbreaking qualities.

And if someone is already using "lightyears" as a measure, I think that's already an amount of improvement which deserves a time-based phrasing.

Anyway, I see good points for both and I am no longer interested in this. Take it or leave it. I don't care anymore.