When you don't know One Piece, it's natural for you to believe these things
You can think a fight between Blackbeard vs. Akainu, wouldn't destroy the ship, but the reality is different.
Lucci vs. Pre-TS Luffy, the fight almost destroys the ship, and Jinbe vs. fodders, Jinbe almost destroys the ship. Of course Akainu shouldn't be capable of putting a decent fight against Blackbeard before losing, but the people who know One Piece, also knows that the marines are always capable of sacrificing their own forces and their own ships in order to defeat the pirates.