He was insane, but he also created, independently, considerably more innovative works than Edison ever did. He worked largely alone and made things in isolation things Edison or his team could not have conceived of. And seriously, inventing AC power (and motors and radios, etc) is more than enough to eclipse anything Edison ever personally accomplished.

He was insane, especially later in life, and before that definitely eccentric but this doesn't mean he wasn't an amazing inventor and bonafide genius. Yes he tried to sell a death beam to several countries and thought he could talk to pigeons when he was an old man and out of his mind, but that doesn't mean his whole life's work was imaginary. Also that death beam was one of the first conceptualization of an electromagnetic particle accelerator so even in his insane state he still came up with amazing science.

Edison was a business man and a marginally successful inventor in his own right, but most of his patents are improvements on old designs from others improved by himself and his team... mostly his team. We can give credit to the proliferation of many inventions to Edison, but not really the creation or imagining of those inventions, just the implementation and refinement of them. He was the Steve Jobs of his day: he sees the possibilities, he refines the existing technology and then pretends he invented it. He then rigorously defends the half truth through litigation. Steve Jobs didn't invent smart phones, portable music players or anything else Apple sells, and Edison didn't invent the light bulb... or almost anything people credit him with.

But Tesla actually did invent things, he was not a business visionary like Edison but he was extraordinary at seeing how the universe worked, a mind comparable to Einstein or Newton, but without their luck when it came to getting and retaining patronage because of his lack of social skills and tendency to isolate himself. Then again Einstein was kind of weird and Newton was full of crazy too.