I'm not sure why you need to prove that it creates negative effects to say that there is a better option. Is UBI better than nothing? Probably quite a lot. Better than a JG? No, I don't think so.
This story very much demonstrates that giving people jobs helping the community rather than just money is a better option. They were both productive and happier. So much so that they didn't want to stop.
I'm sure the nature of the job probably had something to do with it. If these jobs were in call centers for debt collectors they probably would have quit en masse and been happy about it.