Man, all of that sounds awful for those coworkers and customers. But it isn't GPs problem. It isn't their company. He doesn't employ them. He isn't responsible for their experience. Put the blame on their poor experience squarely where it belongs: management. Why is shitty management letting some underperformer ruin things? Super convenient to claim personal integrity and shift the blame to the underperformer when management is clearly not demonstrating personal integrity and protecting their team and customers.