You're right to point out that Tesla has years of pent up sales, but it is still true that, whatever their sales are, they are more impressive in a market where other automakers are declining than they would be in a market of overall double-digit auto sales growth.

That's like saying Amazon won't continue because I can walk to Walmart. If the numbers won't continue give specific facts relating to the market of teslas vehicles. Unless the vehicles become failures themselves, a better alternative is made, or tesla suddenly bottoms up, 400,000 new vehicles isn't too bad.