A good analogy for the 1950's Browns and Lions would be the golfers Jack Nicklaus and Lee Trevino. In head to head play in big tournaments, Trevino almost always seemed to beat Nicklaus, but Jack won more than Lee, even if you don't count Jack's wins before Lee played on the PGA tour.
Jack Nicklaus won 6 major championships, including the Masters three times, before Lee Trevino joined the tour in 1967. Lee won the 1968 U.S. Open in 1968 and Jack finished 2nd. Lee beat Jack in a playoff in the 1971 U.S. Open, and won the 1972 British Open when Jack, going for the grand slam after already winning 2 majors that year (Masters and U'S. Open), finished 2nd to Lee. In 1974, Lee Trevino won the PGA Championship in a final day battle with Jack Nicklaus. Jack finished 2nd.
Nicklaus ended up winning 18 professional major championships to Trevino's 6, and Jack won 12 of those majors after Lee joined the PGA tour.
Like Jack Nicklaus, the Cleveland Browns had won everything before Detroit started their championship run in 1952, but only counting the 1950's, Cleveland also won more than Detroit, but with the same number of NFL championships during that decade. The Browns won 20 more regular season games than did the Lions during the 1950's, and 3 more conference championships. Detroit did have three losing seasons during the 1950's, whereas Cleveland had one.
So, like Jack and Lee, who is greater, the team that wins more head to head, or the team that wins more overall?