Also, in syq, a connection is the unit of independent transfer work. Probably it would be possible to get higher bandwidth per TCP connection by some kind of multiplexing, but that architecture would be more complex and probably not have many benefits.

There's also MPTCP (multipath TCP) which is even supported on mobile devices these days. So for example if your device has both a wifi and a cellular connection, and both ends of the stream support MPTCP, you can increase throughput/failover by combining multiple interfaces.