That is completely wrong.
The IPQ8064 (and its 1400Mhz Krait CPUs) should be able to route and NAT at a far faster rate than 455Mbs without any hardware NAT acceleration.
If you look at the threads on here that deal with other IPQ806x based devices (like the Netgear R7800) you would know the reason for the slow speed is because the IPQ8064 is one of the few devices with CPU clockspeed control and the default "ondemand" CPU frequency governor keeps the clockspeed at a lower rate than it should when under load.
See this https://forum.openwrt.org/t/r7800-performance/15780/29 post for more info.