[zx10guy]

You have to understand that WiFi is a half duplex technology. What this means is only one device can talk on the air space at any given time. This includes the access point. This is why there has been a push to have ever increasing speeds with the various wireless standards that have been coming out. The faster a device can transmit its data the sooner the air space is available for another device to transmit. When you start adding more and more devices to the wireless network, the potential you will cause all the other devices to wait increases as a result. The problem also gets exacerbated with any local interference which will decrease the optimal transmit speed of a device or if a particular device is too far away from the access point to transmit at peak speeds. The greater the distance, the slower the transmit speed and therefore the longer that device hogs up the air space.

While there are newer technique such as multi user MIMO which came out in 802.11ac phase 2, not all devices support this.

The best wireless network to use is one with multiple access points which act as a single logical wireless network. There are plenty of choices out there such as Eero, Netgear Orbi, Linksys Velop, Google WiFi, etc. These systems are best as there are multiple access points to share the load of wireless clients therefore decreasing the likelihood of congestion. The other benefits of managed systems such as these are true roaming support, auto non-interfering channel selection, auto RF power management, etc.