Tesla workers are paid about the same as UAW workers are. Could be a bit less in some cases, could be more in others. Paying someone slightly less is not mistreatment. Is it surprising that companies that have grown fat selling gasoline powered cars with huge subsidies for decades can pay more than a start up?
As far as disagreements between the management and the worker - do you really think Ford and GM have never been sued for mistreatment by any employees? Any company with 100,000+ workers will have instances of management mistreating workers. That's an unavoidable part of organizations run by humans.
Going by that criteria, there aren't many car companies you could buy from from in good conscience. And any idea that the Big 3 in the US are good companies just because they are unionized doesn't hold up to scrutiny.