I came from an ADT Pulse system (~2010 timeframe, so ancient Z-Wave--by iControl).
The Z-Wave stuff was pretty rock solid--all my things worked like I expected. I just ran into issues with the platform (no cool stuff, all old devices, no enhanced functionality--then, suddenly, I couldn't make updates and 2 months with Tech Support say "delete it all and start over"; so I did. With Hubitat
).
In any case, Z-Wave CAN work fine enough (ADT's problems weren't the radio protocol).
As for this:
Um. Yeah. It would be nice to come close to having THAT problem. My puny $200K (give or take) shack and I are likely to run far from they toys found in $5m houses. Besides, the toys in $5m houses are probably WAY overpriced because, when you're spending that on a house, what's another $200K??
So. I really don't see that Z-Wave is "terrible" per-se.
Currently, with the Hubitat and, possibly, the new 700 series chip, there are some issue. I'm hopeful that the 2.2.4 release will get those resolved to the point I don't have to double check all my lights and locks to make sure they worked. And, the things said so far about what they've got coming give me hope that will be a HUGE improvement.
As for Zigbee, I now have a few buttons and stuff. They seem to work well. And, I like having that as an option. However, I keep hearing all KINDS of issues if you have Zigbee lights involved--as they apparently try to repeat but end up screwing everything up when they do that (so, most of those end up relegated to a second, dedicated hub!!).
As for Wi-Fi: Yikes! I have all my home devices hard-wired with Cat-7 cables whenever possible just to avoid all the mess with Wi-Fi. If I was in one of the $5m houses, my neighbors would be a mile away and out of Wi-Fi range, so it might work OK. Alas, I can see like a dozen other Wi-Fi networks from anywhere in my little shack--so I can't imagine that's a great place for 50-100 IOT toys to battle it out. 