In reply to a post by beneix:

Vimeo has an option to upload from Dropbox. Since I can limit the upload bandwidth to Dropbox, I want to try this to see how the transfer then happens from Dropbox to Vimeo.

This has helped - I set Dropbox to use around 75% of the theoretically available speed as per Speedtest. With this, my download speed seems not to be affected. Here's a good explanation on Quora.

I didnt think it could be fixed except by some form of QoS or throwing more bandwidth at it?

If you have 1mbps upload then anything syncing will naturally use the maximum allowed, in effect slowing everything else down. Same with downloads although not as bad as you have more room to play with