inconsistent Throughput, RTT, packet loss on TCP service (FTP)

Hi, currently I do a routing simulation on GNS3 with FTP as reliable service and Video streaming as unreliable service together. I'm using 4 different scenario on routing: no link down, 1 link down, 2 link down, and 3 link down on every route that used to send packet. Theoretically, the more link down the QoS or data will get worse, for example QoS with no link down will be better (higher throughput, less packet loss, and less delay/RTT) rather than 3 link down (in reverse). The Video streaming result is come with correct result, I mean with it supposed to be. But the FTP result didn't come as I hope, the throughput, RTT, and packet loss has inconsistent result on every scenario. Sometimes 1st scenario is worse than 2nd scenario, or 4st scenario is better than 2nd scenario. Is it normal or TCP service actually doesn't affected by how often link dropped even the link is used to route packet?

Thanks