I can't imagine it's the high number of (IoT) clients that is the problem - it is the high power that the AP's use that causes the issue.
WiFi goes two ways - the AP talks to the client, and the client has to talk back. Clients don't have the high transmitting power that an AP has, and actually the AP won't need this high power. After all, if you use a bullhorn to reach your backyard, but the guy over there can't talk back, there is still no communication.
The solution would be to set the AP's to a lower transmitting power, enough to cover the house but not the street.
That would be the ideal solution, but they'd have to adjust tx power on all of their devices. Or at least a significant number of them. Which might prove problematic, since most of them don't allow manual adjustment.
WiFi goes two ways - the AP talks to the client, and the client has to talk back. Clients don't have the high transmitting power that an AP has, and actually the AP won't need this high power. After all, if you use a bullhorn to reach your backyard, but the guy over there can't talk back, there is still no communication.
The solution would be to set the AP's to a lower transmitting power, enough to cover the house but not the street.