I'm not at all suggesting that Huawei (or TP-Link, or anyone else) are actively attempting to subvert security systems or intentionally adding backdoors. In that sense it's probably right to conclude this is ignorance.

The problem is that an attacker, especially those with the backing of a nation state, can trivially attack those insecure supply chains and install backdoors or data exfiltration.

As for whether others are as bad, I think the sort of audit that was done on Huawei is done for other companies attempting to sell into that level. These audits are not really about looking at the code – sometimes they do, but you're never going to get a useful security audit of 10s-100s of millions of lines of code. They're more about the security posture of these companies, and in that way, Huawei failed.

I do expect that Cisco, HP, other network hardware vendors are better at this. Do they still have crap code? Sure. Do they still have security vulnerabilities? Of course. Could a nation state still get a backdoor in? Probably. But would it be significantly harder to do, easier to detect, and easier to resolve? Yes, and that makes them better suited to critical infrastructure.