OK, I'm not going to dwell on the essential details you left out or spun to create this a narrative. The most important object is your assumption that a continued telephone monopoly by old school AT&T would have led to Western Electric being a player in commercial 5G. But that implies that there would still be a single provider of phone services in the USA, that would provide a guaranteed market for western Electric products, and that provider would be an aggressive player in deploying new-tech cell services. But old AT&T's business was stodgy, uncompetitive, and conservative at offering new services, as you would expect from a monopoly. For years, they kept long distance rates extremely high, even which automated switching systems dropped their internal costs down to the level where they were nearly the same as local costs. Western Electric's product development was focused on increasing the reliability and cost-effectiveness of deploying existing phone services. If you think cellular service development in the USA lagged some other countries; it would likely have been far worse with a continuing Ma Bell monopoly, where they would have been very reluctant to cut into the extraordinary profits coming from their landline and long-distance services.