"Two is one, and one is none" is a phrase I've heard for critical survival equipment in several contexts. For example two regulators when scuba diving,
two tie-offs when securing gear to a pack,
It's not like they had any systems competing, unless we're talking competition between Boeing and FAA, where one fights for profit by destroying evidence and fudging results, and the other tries to fight for safety (nominally).
P.S. It didn't start with McDonnell-Douglas acquisition - 737MAX is not the first 737 with deadly design failure - the first one was the original one. Except there Boeing also destroyed evidence from wreckages to hide the issue.
