That scene just before the credits

that may be Battle of Noryang (that was after Myeongnyang), not sure if Koreans had turtle ships though

The movie failed to explain the extra advantages of "The Turtle Ship". The final scene tries to show off some of its prowess.

The major advantages were

(a) Largest of the korean warships with up to 3 decks
(b) Covered in spikes to make boarding deadly for japanese who had to jump off higher ships and land on turtle ships
(c) Shielding of all personnel on deck to fend off japanese rifle attacks
(d) Dragon's mouth could project smoke to camouflage ship's advance.
(e) Dragon's mouth could project deadly gasses to help kill enemies
(f) Heavily outfitted with Cannons on the sides and fore (in the dragon's mouth) and aft.

Normal advantages shared by all the High-Tech Korean Ships including Turtle ships

(a) U-shaped hull for 360 rotations in-place
(b) Relatively high speed at > 3mph top speed with oars
(c) Heavily outfitted with cannons on both sides for long-distance warfare (first ships to be designed NOT to engage via hand-to-hand combat.)
(e) In general the Korean ships were more rugged and built for ramming as a way to sink enemy ships and the turtle ship was no exception.