Well, Coytte, was not gen Zheng's priority enemy, Qing government is, they're after Zheng's behind. the nine months siege was to exhaust his resources, fresh water that was, and to save Zheng's men, expecting Coyett to give up.
Well, You don't surrender, you died!
Of 2,000 Dutch soldiers, 1,600 were killed in the end.
Merciful Zheng let the remaining Dutch to go free, a big mistake,
The Thief, 'your county' came back after Zheng's death, invaded and stole Keelung, a northern City of Taiwan six years later...
'Your country', committed a crime, exactly like German Nazi in May of 1940's invasion of Holland. If you're implying the braveness of Dutch soldiers in the battle of fort Zeelandia, well, Dutch surrender to German only 5 days after Nazi 'enter' 'your county'!
Well, it's good that there are no Dutch troops on the street of Tainan today, and as the American would say, Gen Zheng really 'kicked some Dutch azz' in Jan, the year 1662.