User identification by device ID, as well as by IP address, is hardly effective against abusers using multiple accounts. At least it can be easily circumvented by using emulators or other devices.
In general, it's worth noting that the struggle of casinos with abusers is endless. Casinos will always improve their security features, but abusers don't stand still and are always looking for new workarounds.
Now this method can indeed be manipulated easily using many different devices, but still using the same network and to create different IP networks will also cost more even if you use some kind of emulator etc.
Now with the help of AI there will be more ways to detect all these multi-account manipulations, but some new ways may be applied.
And now KYC manipulation can also be done easily with the help of AI even though KYC requires a face photo or a face video, all can be manipulated.
It's getting more complicated but of course there will always be more sophisticated ways to overcome all the manipulations related to Devices and KYC.