Aside from wanting to protect its citizens from foreign spying; I have to wonder if another reason for the US's curtailing Huawei is to simply eliminate the competition?
There's no shame in the hypocresy. It's a blatant attempt to damage Huawei.
I have no sympathy for what the Chinese government does to subdue everyone under their power, but the Americans seem to have been historically better at playing the victim and getting away with it while still managing to curtail on others.
I don't get why people are so hung up on proof though. There doesn't have to be proof. No one who I've talked to in the networking industry cares about proof (this includes myself). Hell China already bans companies at will. The only thing that matters is enough of a non-zero chance of Huawei releasing malicious firmware updates to select targets in the future. Judging by their inability to have firmware revisions that completely match in functionality who knows if they're already doing so at a smaller scale.
The reason you look for proof is not that it gives you 100% security. It is the process of finding proof that helps us understand how secure a product is and what vulnerabilities need to be addressed. GHCQ's through examination of Huawei devices found problems with version control, and Huawei promised to fix those problems. This is how security could improve.
I think you also vastly underestimated how difficult it is to do version control for hardware due to extremely complex supply chain. If you examine products from any other brand, the situation is likely to be worse. I'm not suggesting Huawei's problems are acceptable. However, it is a misguided approach to decide which products are secure purely based on national origin rather technical merits.
Anyone using factory shipped firmware for the entire life cycle of a device is negligent. I don't think I've had firmware functionality mismatches with Cisco/Juniper/Arista/etc gear especially since we track hashes and store images locally.
You don't simply leave a gate open because the attacker can scale the walls. I don't see any reason to make it easier for the Chinese government to implant itself in our networking infrastructure. Being able to directly provide and modify Huawei's firmware sans resistance allows them far greater flexibility than what they would have attempting to compromise <insert_us_vendor>'s development resources (not that it's impossible, not even remotely saying that).
I don't like the idea of having important infrastructure like this in the hands of any foreign manufacturer. Not while there is indeed evidence that government try to enforce backdoors in tech equipment.
Wouldn't this also have been considered as part of the decision to ban Huawei? And yet the administration proceeded anyway.
[1] https://www.rt.com/news/461918-chinese-company-f35-parts/