I don’t mean to be argumentative, but I want to genuinely understand your comparison: Scottish English and American English are the exact same language (sure there are differences that can be assimilated to regionalisms), but Spanish and Portuguese are two different languages (they come from the same root ane grammar is similar, but not the same, the vocabulary is generally different (though similar sounding)).

When you compare Scottish English and American English, I tend to see a relationship more similar to Brazilian Portuguese and Portuguese from Portugal.

Cheers, mate!