Yes, I have flown a galleon countless times. I'd also like to point out that I engineer on Zill's galleon in competitive play, so I'm likely more aware than the average player of what galleon crews go through. Now, yes, the galleon has to turn. Phoenix claw on a galleon (or most ships really) is a 100% necessity. Whoever told you that you need to be within 750 meters to use the hwacha was sorely mistaken, I'm afraid. It fires up to 1.2k, and as long as you have heavy ammo loaded in, you can hit at that range with a bit of practice. A gatling gunner may target your hwacha, but it's fairly difficult to consistently hit a heavy gun with a gatling gun, especially while both ships are moving. Not to mention the galleon crew should be focused on not letting their guns get destroyed, so they'll be repairing them while this is happening.
If your hwacha is gone before the galleon has even turned to fire, something is going seriously wrong. Having an engineer downstairs absolutely does not mean the hull is being sacrificed. You should have two engineers; one upstairs on the hull and balloon, and one downstairs on the guns and engines. Again, if your galleon is dying before even firing a shot, something is going seriously wrong.
I didn't "silently agree" that the galleon cannot outrun its pursuers, I simply said that it doesn't need to. If you'd like to try outrunning your pursuers, the galleon certainly can. It has poor acceleration, but a fairly high top speed. The only reason it's generally a bad idea is because then your broadsides are no longer facing the enemy. Of course you have things like tar barrel to help mitigate this.
You keep coming back to your point of "have their ship evaporate at a moment's notice" ... I'm not sure what's happening in your galleon matches, but the galleon should never be evaporating at moment's notice, and that's almost never my experience on a galleon.