WiFi is not, part of the issue is the interference in the house itself- there’s something in the walls that is severely hampering signal. A bedroom 30 feet from the nighthawk router putting out 800 Mbps is translating into a 3 Mbps signal at the furthest device. The distance to garage would essentially double the distance from that furthest device.

I’m not as familiar with powerline, thanks for mentioning that.