English itself is considered a germanic language so it actually is easy for english speakers to become proficient in german and vice versa.
However mastering is another story. In this case the similarity of the languages causes you to make a lot of wrong assumptions.
I speak both English and German as a foreign language, so I can observe both sides of the struggle from a neutral point of view.
I understand what you mean. It does actually make sense. Some languages may be easier to learn at a casual level, but harder to be truly good at.
at the very least, many words are similar in both English and German.
e.g. apple, apfel