They also cause explosions/shockwaves, though, not just melting damage. It seems very wanked to assume he melts the entire surface, especially since it could just melt one area and flatten the rest (like massive explosions do).
Edit: Reading the manga again, it seems like you guys are mostly off the anime's visuals and applying it to the manga.
Boros'
energy blasts rarely melt stuff.
Edit 2: One of the other justifications is that it would have scorched the Earth according to a databook statement. If it's scorched, that actually means blackened/burned, not melted.