Hello. I am a native English speaker and a grammar nerd.
1) The word rather would not be a good fit in the first example sentence. We would use the term “to avoid”. A good revision of your example sentence would be, “He walked in order to avoid getting stuck in traffic”. More casually it could be stated, “We walked so he wouldn’t get stuck in traffic”
In the second example sentence, the word rather works. It would be correct to say, “People should be concerned about themselves, rather than meddling in other people’s affairs.
2) It seems there should NOT be an apostrophe in Picasso. An apostrophe signifies possession, not plural. Such as, “Those memoirs are Picasso’s”. So it would be correct to say, “These paintings are all Picassos”