He invented the brushless motor and types of transformers that were instrumental to building Westinghouse's empire. When Westinghouse was running low on money Tesla tore up the patents he'd sold to him to save the company.
Tesla was definitely not a "bad decision for investors", the ROI for his inventions is some significant fraction of the economic value of the global electrical system.
But yeah, a couple of his projects failed at some point. Surely a terrible investment!