Not saying TSLA has no risk: for one thing, they still have not figured out how to scale up production. But in general, I think we tend to overestimate the incumbents' advantage. Most incumbents have too many old interests that hold them back. There is an article [1] about German automakers' unwillingness to commit to EVs because the profit from ICEs are way way higher than that from electric ones because of ICE's complexity.
(Similarly, this is the reason why most of the wind farms in China are not connected to the national grid, because the existing power plants do not want to shut down and lay off workers.)
[1] http://www.spiegel.de/international/business/german-governme...