Sure you can grow groups in Signal.

Up until you allow to join that one member that will leak every single thing you wanted to keep private.

But giving law enforcement first-class access to groups helps them avoid law enforcement how?

Not sure my English skill is enough to understand this sentence.

Who exactly gave anyone first class access to anything?

And no, private groups in Telegram are still fully visible to the state-supporting Telegram corporate employees.

This is like saying that an email provider has access to your emails. Not even trying to argue with the rest of implications. So what? You're still avoiding the point. No service can protect you from the real world. You must avoid real world issues yourself. By either using private features of apps, or by not participating in public communication, or by using apps that prevent you from participating in public communication etc.

Someone cut a hand with a saw when cutting a board. You saw that and thought "that saw manufacturer is at fault, I'd better use a saw from another manufacturer". What's happening really is you choosing a knife over a saw. Also it's very probable that people like you are not ever going to try to cut a board. That's what choosing signal looks like to me. I'm not judging you for choosing a knife or for avoiding boards, but it's worth it to understand the differences.