Not a good advice at all. As he cannot reach "normal/decent" speeds, wider channels, will just utilize larger spectrum without any reasonable gain. With 2x2 MIMO he should easily reach far better real throughput than 30Mbps even with 20MHz.
My lucky guess would be to check SSID settings and check if WMM is enabled, and TKIP is not in use. For me it looks like connection speed limit to 54Mbps.