You did a very poor job if it if that is what you took away from their documentation
It is a private company- So are the manufacturers of every piece of hardware in your home, homelab, data center, etc. SO WHAT?
You must install its application on each of the devices designed by that company. Same as for lots of other software, similar to what you do with wireguard. Their code is open source (except for the daemons that run on closed source platforms) and you can actually self host tailscale yourself if you want using an opensource product called "Headscale"
The connection through Tailscale is slower than the connection with Wireguard. Patently untrue. You clearly didn't read any of their documentation. Tailscale sets up direct peer to peer connections.
You depend on the profitability of the company. Only if you refuse to self host, otherwise this is also patently untrue. The Tailscale software for open source platforms is fully open source as is the Headscale server.
Why do you insist on creating FUD for something you can't be bothered to learn about?