Likewise, you can pretend to be sure it’s a backdoor without any proof and then also believe there’s more that’s not been exposed. Signal is also US-based, by the way. What software do you trust not to have vulnerabilities that could be abused by the likes of NSO Group and why?
A vulnerability allowing to exploit an app is not the same thing as a backdoor. Moreover, being able to gain full access to someone’s device does not prove that an app’s end-to-end encryption is faulty. The same kind of exploit most likely could be used to read messages from Signal and definitely other apps.
Has there been any evidence of that? Intercepting the traffic or disassembling the app would show some signs if true.
WhatsApp uses the Signal protocol for end-to-end encryption, so Meta only collects the metadata. Still enough to convict, but better than anything from Putin.
Going by your logic though, what would stop a Five Eyes country like the UK from pressuring the developer of SimpleX into creating a backdoor? Besides, as discussed, even if it were bulletproof, it’s improbable that the victim would have no other apps on their device, one of which could be exploited by the likes of NSO Group. The creators of Android and iOS are also obviously US-based, so your point would have to apply to them as well. From there, if someone remotely gains full access to the device, it won’t matter if you use Signal, Telegram, WhatsApp, SimpleX, or that new Russian thing. However, having e2ee is still better than nothing in that it protects from other attack vectors, like the ISP analyzing the traffic and reporting to the government.