I guess I don't understand this sentence, particularly why 'là' is there. Could 'là' be omitted? Google seems to say 'yes'.
heard as "Nó không dễ như bạn nghĩ" does not have là
Như and là both may mean "as", why the combination meaning the same?
According to my Vietnamese wife "như là" is one word, meaning "as". Vietnamese apparently do not use "as" twice, like in English.
Can any native speakers confirm whether or not this is a common saying?
Yes, and both "nó" and "bạn" can (and usually) be replaced with other words.