Slow uploads of large files

Slow uploads of large files

I'm wanting to use Workdrive for transferring large images and video (we're talking things from 100MB-5GB). I'm running solo on a 500MBit/sec fiber connection. I'm getting upload speeds to Workdrive of no more than about 1-3Mbytes/sec when going through the browser, and even slower than that if going through Truesync. I'd expect about 10x that--a Backblaze backup, for instance, will bam along at 10-30MBytes/sec, so it's definitely not my connection that's in the way.

Running Safari 14.0.3 on macOS 10.14.6, and traceroute to Workdrive is:
traceroute to docs.zoho.com (204.141.42.105), 64 hops max, 52 byte packets
 1  rt-ax86u-3be8 (10.0.1.1)  0.829 ms  0.601 ms  0.577 ms
 2  ip-38-147-4-2.fibre.fibrestream.ca (38.147.4.2)  1.706 ms  1.713 ms  1.553 ms
 3  v211.core1.yvr1.he.net (184.105.226.21)  1.811 ms  1.914 ms  1.872 ms
 4  100ge10-2.core1.sea1.he.net (184.105.64.109)  4.825 ms  4.804 ms  4.908 ms
 5  six2639.zoho.com (206.81.80.136)  9.885 ms  9.872 ms  8.993 ms
 6  10.10.26.81 (10.10.26.81)  9.170 ms  9.881 ms  9.094 ms
 7  * *

Anyone else experiencing pathetically slow performance on large files?