My neighbor thinks that they can increase their 100Mbps ISP speed by having 5 or 6 access points at 2.4GHz in their 1400sq ft (~140m2) apartment.

There’s so much interference that the package dropout rate is around 40% at 2.4GHz usually.

Having a AP in every room can be as significant boost if the walls impede the signal a lot. In fact we have one wall which is especially bad. Stand in front of it or next to it and reception from the front of the house is decent. Take one step back behind the wall and signal drops to less than 10%.

So having the 5-6 AP is not the problem, then shouting at max power is the problem. Especially “gaming” routers tend to do this.

2.4ghz is pretty bad but the 5 and 6ghz bands don’t really travel far. I’m in a dense area and 5ghz works great while 6 has basically no detectable traffic.