Arms race started in response to PED's and then really accelerated when the testing reached the point where teams could no longer slug their way to the playoffs.
Offered the opening we see for the smaller markets to compete. Find enough arms and you can win with average offense with a few real talented position players. The Giants (although not small market) are the poster child for this approach. TB, KC, PITT and Nats and others have been on this bandwagon for years.