‘Symphony in Slang’ demonstrates a perfect use of the “modern” cartoon design emerging in the early 1950s. It wasn’t there for the sake of being there. It had a purpose.
Tex Avery wanted to create a world where a character was completely out of place in the standard world of the MGM cartoon—a world of rounded characters, full animation and pastelled, soft backgrounds popularised by Disney. So he had Tom Oreb come up with a flat 1951 hipster character, living in a flat 1951 hipster world with limited animation. The contrast when the hipster arrives in the Disney-esque Heaven where the characters are puzzled by his modernism is deliberate and damned clever.
There’s no animation in the opening, too, as Avery has the camera move over two backgrounds before getting to any character movement.
Johnny Johnsen was Avery’s background man at the time. While Oreb is giving credit for the designs, notes on finished sketches show notes from Avery to Johnsen, so he worked on the cartoon as well. I wouldn’t be surprise if the opening was entrusted to him.