Maybe. Or maybe it's someone that paid for a complete remodel and some contractor sold them on making every light and outlet and appliance "smart" along with some more we can't even think of, because that's all extra money to them, and then they throw whatever else they can find at it to make it work because really, they haven't ever put so many things on one network before.

I've heard crazy stories about home installers and contractors that didn't really know what they were doing. Everyone starts somewhere, and it's not always with our own home nor with a mentor that actually knows what they are doing.

Or, it's just some person that did it for their own home but went way too far and when they finally got it working (sort of) decided they really didn't want to touch it again for a while, because it was a pain.

Truthfully, either of those sound kinda likely to me.

I don't think the IoT devices will care that their download speed is somewhat reduced and that they'd have to wait a few ms to get access. These devices will hardly transmit or received any data. Likely a lot of switches, wall outlets and some sensors that you'd want a reading from every minute.

The number of clients should not be an issue, the half-duplex shouldn't be as well...