In the context of communication networks, WiFi is a high speed netowrk. It was designed to be basically a "normal" (ethernet-like) network, but wireless. It acts for all intents and purposes like an ethernet network. There are significant requirements that devices need to follow, many include frequently saying "hello" (simplified). The complexity of the protocol to be able to send at gigabit and faster speeds over dozens of meters is significant. Having relatively low latency adds to this as well. If all you need is a few bytes every now and then, that isn't ideal. Having devices in your network that follow older/slower standards is essentially like pulling the handbrake for your network (again, very simplified). But explaining this in detail is also very much beyond the scope of a comment here.

ZigBee devices form a mesh network, which WiFi devices don't do. This means I can have my hub on one side of my house and a bunch of bulbs and smart outlets maintain a backbone through the house for a bunch of low power devices (like thermostats and door sensors) to connect to it.

If you're having a bad ZigBee experience, I recommend making sure your bulbs can serve as a general ZigBee bridge, and not just a bridge for other bulbs of that brand. Otherwise, a well placed smart outlet can serve the same purpose.

I also don't want devices I'm actively using to needlessly compete with random logistical packets from a dozens of devices around my house. I also don't want the devices themselves to need all the power of a WiFi connection when another protocol suited to low power home automation devices is sufficient.

ZigBee/zwave were fine for me, though. I personally haven't seen a clear benefit to matter+thread yet.

My favourite thing about these non-wifi wireless protocols is that devices using them seem to want cloud connectivity a lot less than those that come with wifi.

Zigbee or Thread doesn't actually stop them from adding cloud connectivity, they all still do. But you yourself can stop it. Similar to the "gateway" you suggested with dedicated WiFi, they sell you a gateway for Zigbee or Thread, which then connects to the cloud/internet to allow you to control your stuff. As they would with a WiFi gateway. The protocol isn't "less capable", it's intended use is around (home-)automation. It is low power, low bandwidth and most importantly both are a mesh network. That means that while you have a central point to access them (at least Zigbee has exactly 1), they all talk to each other and for a fully connected mesh. A device doesn't need to be able to see/hear that central point. It can send it through a multi-hop route, and that route is dynamic so when a device leaves (out of power, turned off, ..) the packets basically just find their way. Generally anything that has a stable power sounce will act as a router and forward packets. The low power part means that if you have a battery powered thing (remote switch, thermometer, ...) it can run off a single button cell for like a year or so. With wifi it would last a week, maybe two. The bandwidth thing is related to that as well, as a thermoeter needs to send the temperature and/or humidity maybe every few minutes, or even just when it changes and there is no need for that. That comes with power usage, complexity and many other downsides, but of course a zigbee device can't stream video or something (like a security camera would need to).

When using wifi, any device needs to be in range of the access point. You can have multiple access point but those aren't that cheap, and should be wired in. Devices only ever talk to the access point. When multiple devices talk to each other, it goes to the access point who then sends it out again to the other device.

There are great writeups on the internet, just google "zigbee vs wifi" or something. I'm not gonna repeat what

Side note: you can reply to more than 1 paragraph in a reply. No need to reply three times, but I guess I'll stick with it now.

If I'm gonna install a device by some random manufacturer that acts as a wifi access point inside my network, I also give them full access to my network. That access point can do all sorts of things, and I would describe this as a security nightmare. It also doesn't even have to be malicious: the manufacturer could get hacked, and now the hacker has access to all these wifi access points all over the world, and all their home networks. Fun.