Default TCP congestion control is Reno, but Linux uses Cubic, increased initial CWND and all the other modern modifications. CDNs have their own proprietary congestion controls that are arguably better, but Google has already pushed its own congestion control (BBR) into Linux, so it is just a matter of time until it becomes new default. There is no reason to tamper with these settings unless you are operating Netflix/YouTube, some sort of CDN or unusual (satellite) link.

> Maybe an option to choose an alternative controller via socket options (linux and windows offer alternatives) would make sense in some situations.

Only the server congestion control matters. Client simply acknowledges whatever it receives as soon as possible and waits for more data.