I think there are many custom apps that are better than the built-in apps. Development resources are always limited. The gap that is being filled by custom apps is letting Hubitat developers work on other things (like new apps and drivers), and to focus on the hub itself.
I use very few built-in apps, and over time I've even replaced built-in drivers with many community drivers, that just work better or have more features.
I agree, some built-in apps and drivers could use improvement, but with a community that just keeps delivering, I just don't see this as an issue.