With a reported link speed of 144Mbps, changing channels would not make much sense as the net bandwidth would be around half of that (72Mbps).With respect, Wifi is my job. Changing speedtest sites is going to prove anything whatsoever as we've already confirmed that speeds are acceptable when wired. As well as that, your statement doesn't make sense. The reported throughput is considerably lower than 72Mbps and interference can and does cause reduced throughput.
Since this is a new fttc connection, I'm thinking the link itself is just around 60Mbps and not the 80Mbps as advertised.So what? That's not the issue here. The issue is that wireless doesn't match wired speeds. If the circuit is an "up-to" 80Mbps service (as advertised), a slower service is often provided based on line length.