The network performance of the Pi 1 is definitely CPU bound - even on Ethernet it can only just manage about 95Mbps when the CPU is otherwise completely idle. If the CPU is also busy doing something else such as running Kodi, network performance plummets to only half that at most.
The Pi 2 has a much faster CPU and consequently can achieve much better network performance when the system is under load, and the network speeds don’t really fall much if at all.