"bufferbloat", Airport Extreme, and bandwidth limiting?

I have a somewhat complex network setup at home. I have a Cable connection with 20Mbps down, 2 Mbps up, my own Motorola SB6141 cable modem upstream. Plugged into that, I have a recent model Airport Extreme (802.11ac), and an older Airport Extreme set up with a roaming network. The primary clients are recent vintage macbooks, iOS devices, with a smattering of other connected devices (DVR, windows, Synology NAS, etc.

The problem that I'm running into is that network connectivity has lots of issues if I run a large upload that saturates the outbound connection, e.g. with Dropbox or another online backup tool like Arq. When that happens, inbound traffic gets super spotty, and things like Netflix become unusable. peer-to-peer within the network continues to work fine.

As near as I can tell, these are the classic symptoms of "bufferbloat" and from what I've read, the solution to the problem would be to introduce an outbound bandwidth limit (say at 1.98 Mbps) at the first outbound bottleneck, in this case, at the Airport Extreme (ac) connected to the cable modem.

Is there any way to do this? I couldn't find any kind of bandwidth limitation mechanism in the Airport Utility.