It's hard to have faith that a US-based company will actually protect your privacy.

You don't have to, though? 1) The E2EE Signal protocol is well-audited to be robust. 2) The app itself is FOSS, and there are a lot of eyes on it. 3) The server code is FOSS. Even if they're lying about what code they use, it doesn't matter because it's E2EE. 4) If you think Signal might be bait-and-switching by building from different source code, you'd be provably wrong. They have reproducible builds, so were they to actually try this, it would be like sending up a flare to the entire security community. 5) Literally every single time OWS has been subpoenaed, the only information they've been able to provide is extremely basic metadata like server connection times.

You have no idea what you're talking about, I'm sorry. There's functionally less "trust" here than any messaging application on the planet. The network effect remark is at least valid and can be debated (although I personally have zero friends who use Telegram and at least several who use Signal). This one is just so, so wrong that it's not even up for debate.