This seems to assume that the 5 Eyes alliance has backdoors in products by the competition: products by continental European companies (Ericsson, etc.) that don't have a notable history of this. That's a strong assumption to make.
I'm not suggesting the companies are compliant, the 5 Eyes Alliance probably doesn't want to give up it's cheap and easy access to telecom hardware ie: information dominance. The executives of Cisco back in 2014 lamented how all the Snowden leaks about backdooring their equipment boosted Huawei: https://venturebeat.com/2014/08/13/nsa-spying-tech-companies...
“This week a number of media outlets reported another serious allegation: that the National Security Agency took steps to compromise IT products enroute to customers, including Cisco products. We comply with US laws, like those of many other countries, which limit exports to certain customers and destinations; we ought to be able to count on the government to then not interfere with the lawful delivery of our products in the form in which we have manufactured them."
