Mostly grousing about my specific situations.
Turns out my phone (LG G4) connects to my home WIFI at around 50 Mb/sec; pretty pitiful (and I don’t know how to get the phone to tell me what speed it connected at; that’s measured at Ookla; but my household WiFi is enough faster than that that it’s going to be reasonably accurate). In theory I should be able to get 20 times that, but I think the phone doesn’t support high enough WiFi specs.
Then, when I turn on VPN (OpenVPN, TUN, TCP) terminating at my router, that drops again, to maybe 7 Mb/sec. However, I can still get that 7Mb/sec from the local library, which blocks most types of VPN connection (no idea why; but this configuration plus using port 443 makes it look essentially identical to an HTTPS browser connection, so few people block it). (The default VPN on the phone is faster, 30 Mb/sec or some such, but using 40-bit encryption or something really embarrassing like that. That one is also blocked at the library.)
Even the laptop connect seems slow; 300 Mb/sec, on a brand-new laptop that says it supports 801.11ac and an ASUS RT-AC66U which says it supports AC. (This is sitting in the same room with, or on the opposite side of the wall from, where the WiFi hangs on the wall.) For that matter the laptops reports an AC connection. I’ve ended up buying an Amazon dongle that plugs into the USB-C port and gives me three conventional USB 3.1 ports and a gigabit Ethernet port.