I've run adb devices and adb push some-stuff /sdcard, and both commands take several minutes. Once adb push gets started though, it races through the file, so the throughput is fine. It just takes an extremely long time to get started on processing the command.
$ adb --version
Android Debug Bridge version 1.0.39
Revision 8.0.0_r17
$ uname --kernel-name --kernel-release --kernel-version --machine --processor --hardware-platform --operating-system
Linux 4.13.12-1-ARCH #1 SMP PREEMPT Wed Nov 8 11:54:06 CET 2017 x86_64 unknown unknown GNU/Linux
The phone is a Samsung SM-A300FU (aka. A3) running a recent LineageOS.
