Mit dem Messwort ist es ganz pauschal gemeint,also irgend 4 große Häfen in Europa.Aber ohne dem Messwort bezieht es sich dann auf die bestimmten 4 großen Häfen in Europa die man alle nennen kann.Hier,,Hamburghafen ist einer der.."ist offenbar nicht pauschal gemeint also ganz bestimmt ohne,,ge".Hoffentlich hilft dir meine Antwort;-)

1.In terms of Chinese Grammar, Numerals can be put directly before nouns to act as ordinal numbers. e.g.一月，二月，二姐，三弟，二年级 2.“数词（number.）+大/小+名词(noun.)”is a special structure in Chinese,and just like 1. 1)It means the large/small ones which is ranged in some ways in congener.just like your example. e.g.路易威登是我最喜欢的三大品牌之一。Louis Vuitton is one of the my most favorite three brands. e.g.她是中国的四小花旦之一。 She is regarded as one of the "Four Young Dan actresses" in China 3 ..“数词（number.）+大/小+名词(noun.)” is a set phrase. e.g.五大洲（Five continents）四大洋（Four oceans ） e.g.亚洲四小龙（Asian's Four Little Dragons /Newly Industrial Economics）

“四大港口”是“四个大港口”的简略习惯说法，“个”习惯上不用；如果加“个”，反而不自然。

One of Europe's four large harbours. One of the world's three great tragedies. One of the seven pillars of life. Phrases like these don't take measure words in Chinese (or Japanese).

最 means the most. It should be a single one like Shanghai is the biggest city in China.上海是中国最大的城市。 If you use 四大 or 五大, it mean one in a few . there is no comparison here..