It is entirely true that all models from all manufacturers are compromised by spy agencies.

I think there's a little bit of space between "spy agencies employ systems professionals that know the guts of a component's security and tricks to bypass it" and "every device firmware has a double super secret protocol for sidestepping all of its security features".

However the worst offender by far is Cisco even though they’re “American”.

Sure. I'm willing to believe that Cisco, specifically, has relationships with the Five Eyes network such that they make monitoring their traffic easier. Even then, there's limits. One thing to say techniques exist to bypass security. Another entirely to know what those techniques are and whether they're practical for application at universal scale.

One of the more chronic problems that big spy agencies have is sifting through all the spam and bullshit and empty chatter. Decryption takes time. And you can't monitor everything, everywhere, all at once. The bigger sins of Cisco are in how they expedite access on behalf of their agency partners, not that they fail to produce perfectly hack-proof hardware.