The archaeologist had spent years searching for evidence of the ancient trade route based on written historical accounts alone. ______,…

The passage sets up two contrasting methods and their very different timeframes, years of searching using historical accounts versus a single afternoon using satellite imagery, and in comparison is the natural way to frame the second method against the first. That is signals a restatement of the same idea, but a different method with a different timeframe isn't a restatement. Granted signals a concession before pivoting to a counterpoint, a different rhetorical move than a straightforward comparison. Otherwise would suggest an alternative outcome that didn't happen, which doesn't fit a sentence reporting what actually did happen.