Anyone who has seen what the Greeks and Romans had for “mirrors” would know that reflecting and focusing the sun’s rays into a long distance incendiary device was a ludicrous notion.
In high school some 55 years ago, the myth of the mirrors was taught as fact to illustrate the power of geometry.
Like my Aunt told me: The sun in Phoenix is different from the sun in Idaho. So the Greeks used a different sun is all.
It could be done, actually. They used to coat their ships in pitch to keep them together.