Sorry for the delay in reply, forgot to circle back on this one. Trying not to disagree but this is not false advertising. Meraki has always followed an MVP philosophy and the hardware typically has greater capabilities than what is supported in the firmware at FCS. Many times the additional hardware capacity is leveraged in time, but sometimes not.
The APs are capable of supporting 160MHz channels, it simply wasn't implemented due to lack of demand and it never became practical in typical enterprise deployments. As you pointed out this thread is a couple years old and 160MHz channels (still) have not become a thing in 5GHz. There has never been significant client support for this, and there are too many issues (DFS overlap, etc) that have prevented 160MHz channels from ever being useful or practical for real-world channel plans.
We do all love the idea of 160MHz channels, and with WiFi6E it'll be great in the 6GHz space, but 160MHz in the 5GHz spectrum IMHO was more of a headache than it was worth. And with the limited client support there never was much demand for it and 80MHz channels was basically where the technology topped out (practical perspective, not theoretical of course).
I'm not on the development team but I can imagine there wasn't any reasonable ROI to develop, test and deploy 160MHz on that generation of APs and firmware.