Both the East Frisian and the Helgoland were Helgoland-class battleships. Why does the East Frisian have a rating of 6.3 while the Helgoland has 6.7?
Probably the extra 88mm AA guns. There isn’t a lot of rhyme or reason as to why there is a slight BR difference amongst ships of the same class, but that and a slightly higher crew count or the only differences.
However, sometimes event ships get slightly more favorable BR’s. I assume that’s so people will grind for it, even if it’s mostly a copy-paste.