There are reasons other than a huge home. I run Z2M on a ConBee2 for Aqara devices and for its wide ranging ability to support very new and not so mainstream devices. Extreamly stable. "Flakey" is not my experience with Zigbee at all.
I run a second controller on HA with ZHA becuase of a few devices that are stable and work so much better in ZHA than they do in Z2M. Six of them are not compatible with Hubitat at all, and one isn't stable on my Hubitat hub.
The remainder are joined to Hubitat directly because they work fine there, and I have no reason to move them off Hubitat, just to have to bring them back into Hubitat where I do 90% of my automation.
I keep the channels relatively evenly spaced, but honestly I didn't put a lot of effort into the choices. Just use what works well. Experimentation may be necessary. Some claim that you cannot have Zigbee radios too physically close to each other. This is not true. I have a few of them just inches away from the other.
Main Hubitat [CH13]
Hue bridge [CH20]
ConBee 2 on HA [CH15]
Nortek HUSBZB-1 [CH25]
It's not always the case that an integration isn't available from the community on Hubitat, but sometimes it just works better on HA, is more stable, or I prefer the way it was built and its features on HA, versus HE. Choice is good.
Is use the following integrations on HA that I either cannot get on HE, or prefer the HA version.
August - I think there's an HE community version, but the HA version is very stable.
Flo by Moen - I use both HE and HA versions. There's a flow rate measurement that wasn't available on the HE version. Maybe it's there now, but I never bothered to switch the automation becuase it works well as is.
Govee - The latest HA version for local control is very stable and responsive. The HE version doesn't work for my particular light string.
Hyundai/Kia Connect - The feature set on the HA version is huge, the code is mature and it gets regluar updates. The HE version is much newer, doesn't support as many vehicles and features, and isn't maintained to the same level.
Z2M - For the reasons mentioned above, this is a very valuable asset. There was some development of Z2M on HE, but the HA version is very mature and feature rich.
MQTT to Switchbot - There's offical support on HA to connect Switchbot bluetooth devices, but there's a community method using an ESP32 D1Mini. I have two of these boards in my house. It lets you bridge multiple Switchbot Bluetooth devices to WiFi and send their output (or command bots) via MQTT. In HA, it just works so easily once you have the boards programmed and it's super stable. No range issues or drop-offs that some people complain about with the official supported Switchbot integration. I have 5 of their all-in-one motion/light/contact/button devices, and one of their bots. Super stable, and pretty responsive for bluetooth.
Nest Protect - Not available on HE and the latest HA version is much easier to use and more stable than the Homebridge plug-in I was using before.
Oral-B - Not available on HE. Lets me track the use of our toothbrush. Getting the boy to brush his teeth regularly is still a challenge. This lets me know if he did it and for how long.
Sense - Not available on HE
Xiaomi Miot Auto - Not available on HE. Connects my Qingping AQM Pro to HA and HE.
Yolink - I have this connected to both HE and HA. The HA version uses a different method to connect. I like having both for a backup since this is cloud controlled. Currently the HE version has a minor issue. The HA version is solid.
ZHA Zigbee - For the reasons mentioned above, this is a valuable assest for a few of my devices that won't connect to HE, or are not stabel on HE.