Lots of things are possible once you have an Ethernet jack (such as using a Ethernet to WiFi or Powerline bridge), but very little is possible when WiFi is your only option.
One of my biggest gripes about WiFi-only devices (even setting aside the reliability issue) is that WiFi standards evolve and are deprecated much more quickly than Ethernet. I could plug an Ethernet device from 25 years ago into a modern Ethernet switch and it’d still work perfectly, without slowing down the rest of the clients.
The same can’t be said of WiFi, when the user upgrades their AP, etc. Enabling compatibility modes slow down the WiFi for all clients, not just older devices. And if your device doesn’t support the latest version of WEP/WPA, then you’re forced to either downgrade the security on your WiFi just so that one device can connect to it, or you have to spin up another SSID or AP just for that device.
Another issue with WiFi is the limited number of channels available; if you live in a moderate density neighbourhood, you’re lucky if your neighbour’s AP isn’t stomping all over whichever channel you’re running on. As wireless devices increasingly proliferate, the problem is only going to get worse.
As to your question about using home automation devices, I have exactly two classes of devices in my home automation setup that are wireless: my Z-Wave door locks and my Harmony Hub. My thermostat and window blinds are RS485, my security sensors are wired, my lights and fans are wired (Insteon).
In short, IMHO every home automation device (that speaks IP) should have an Ethernet port. If you want add WiFi on top of that, go for it.