Actually, the name is “Tonto”. Apparently, in Italian, Portuguese, and Spanish, "tonto" translates as "a dumb person", "moron", or "fool". While only a few would be fluent in any of those languages in the American West, Spanish words- for things like food, drink, slang and insults- might be familiar to a fair number of people. Especially the farther west or southwest you go.I think someone ought to do a movie about Tanto where Lone Ranger is even more dependent upon Tanto.
(I also wonder where they chose that name from. The Spanish "Of Course!" or the Japanese dagger, or elsewhere?)
And that fits in nicely with your observation about how the character is often dismissed by most of the antagonists- the clearly caucasian HERO is literally calling him “Dummy” all the time. It plays right into the prejudicial mindset of some of the people they opposed.