The new app is Is definitely missing features, no question. But as far as stuff they’ve added to the old app, the whole smart lights feature is new since the acquisition and has a lot of good stuff in it. And they continued to add to that, such as adding luminance and mirroring and setting dim levels. All good. 
Four years ago they had one hub model and had just released it for the UK. Now there are eight or nine, including the Wi-Fi mesh version, the ADT model, the Nvidia model, And they are now available in many more countries. I know that doesn’t help you as an individual US customer, but it does show there’s been a lot of work done.
There have also been a number of technical improvements, although they’re all behind the scenes. The zigbee implementation, for example, is much stronger and now you can even do multi endpoint devices which you didn’t used to be able to. And they started to add zigbee 3.0 support. Z wave plus is now well supported and they are adding support for the new S2 security framework. They also have much better central scene support. And they increased the number of devices you can have. The platform architecture for parent and child devices has changed completely and opened up a number of feature possibilities, including support for devices like power strips. They also added over the air firmware update capability for zigbee devices.
There have been many new integrations in the last couple of years. Including ring, Arlo, google home, ikea Tradfri, Iris Devices, and a number of other popular ones.
They’ve also significantly increased the amount of local processing, including local integration with the Phillips hue bridge. Those only run through the official SmartLights feature, but it’s a lot better than where it was before the acquisition.
I’m not saying everything has been sunshine and jellybeans, and reliability continues to be an issue, but they clearly have invested time and resources into platform improvements.
But, yeah, the new app still sucks. 
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