The airwaves in an apartment complex can be very busy (even on 5 GHz - forget about 2.4), and a general inability to use WiFi analyzer apps and at times obnoxiously stupid autochannel algorithms aren't helping matters in the slightest. Wired networking wins by default by not being a shared medium. In a busy environment you ideally want a bunch of small, lower-power cells, e.g. a centrally controlled swarm of accesspoints each with a wired connection, like one per room. Progress in newer WiFi standards hinges on two factors, higher bandwidth and smaller distances, so you'll never get the best out of those by relying on a central router only, which usually comes with egregious coverage gaps as well. I managed to get a decent bedroom to living room link (about 9 m across) but you bet I was watching spectrum usage like a hawk and I know all the networks around me.