I won't get into the why but let's take Netflix and 4K movies as an example. You only need 25 megabits to play a 4K UHD movie and the iphone, ipad, apple tv are just players so this is fine.

As to high speed WiFi to hit those speeds all parts must work together and as there are many versions of WiFi radios some don't hit the max speeds. On top of that you see the speed taper off as you move from under 3 meters to further away. This is not a bug.