I can’t blame Leviton for this. Their devices meet the Z wave standard, and they do work fine with Zwave controllers from other brands.
The issue is that smartthings is a multi protocol platform and they have not implemented all of the optional Z wave command sets. They don’t support Z wave scenes (they have their own type of scenes which can handle devices of multiple protocols), they don’t offer any simple way of setting up z wave associations, they don’t even handle central scene commands natively.
The Leviton devices work fine with their own controller and work fine with most of the other Z wave only controllers.
I don’t see how they are responsible for meeting the idiosyncrasies of a multi protocol platform with its own architecture. They might choose to do that if they wanted to, but I don’t fault them for not doing it. They certainly aren’t the only ones. (Fibaro, Sunricher, and even GE/Jasco all run into the same issues with SmartThings.)
People have been asking for a local wallmount keypad/Scene controller that would be natively supported by smartthings since 2014, and they’ve always said they would look into it, but as of yet there isn’t one. Everything that has been done relies on custom code.
With regard to Leviton devices specifically, for some people the easiest thing would be to get a different Z wave hub, use it to control the Leviton devices, and add it as a secondary controller to a smartthings set up. That doesn’t let you use a Leviton device to control, say, zigbee lights, but then Leviton has never promised that. It would let you use the full Z wave capabilities of the Leviton devices, by choosing a hub that supports the full Z wave capabilities of the third-party standard.
I realize none of that addresses your frustration, and it’s a frustration that I myself have been expressing for five years now. First with local scenes and then with central scenes. at one point I even suggested that the smartthings app colorcode the protocols for each device so that if there were some which used protocol-specific features it would be easy for customers to tell which other devices could be used with those features.
But the smartthings design philosophy continues to be that The protocol should be largely invisible to the user, and therefore some advanced device features are not supported.