Ah yes. I'd say that's more a problem with TCP in general than in using multiple connections. The assumption that "1 TCP connection == 1 share of bandwidth" is at best a useful first approximation. I don't know that N TCP streams eating N times their "fair share" is really any different a problem than some-important-interactive-application being given equal bandwidth with some-irrelevant-background-download. (Though it might be a worse problem.)

I'd love to live to see the day that something actually better than TCP (that addresses these and other issues) dethrones it, but given how long IPv6 took to gain traction, I wouldn't be surprised if it didn't happen in my lifetime.