Instead of looking at the situation through the lens of "Tesla vs other car companies", let's take a step back and look at the battle of "electric vs gasoline". The better EVs do, the more charging infrastructure gets built, and the more receptive people are to buying EVs in general. These kinds of effects disproportionately help Tesla; their whole business is electric cars, whereas EVs are only a tiny slice of the pie for every other established car company.
Because there is so much room for growth in the EV market, we're also not necessarily dealing with a zero-sum game right now. Helping other companies sell more electric cars does not necessarily mean Tesla will suffer reduced demand; it may actually have the opposite effect. Even simple lack of awareness is still a big obstacle for EVs: https://electrek.co/2017/01/03/electric-vehicle-adoption-awa...