Just some idea why DE not divide download file into smaller file, something like when need to update 8gb divide it to 1gb and checksum, when download fail we don't need to re-download all 8gb again. save our time to download. save bandwidth to your server. Slow download may was from ISP (Internet service provider), they saw your server comsumtion too much bandwidth and limit speed of your server. This thing happen to me I test it by switch between ISP-net and VPN-net, when switch to VPN speed going up.
Another thing i saw warframe update though port 80, this is bad, because ISP