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.