Still it's the pro-Tesla person that's making the claim; the onus is on them to provide the numbers or if it's not a fair comparison, to avoid it (or clarify it).
That's why I asked what models the other person looked at because so far all of the information I can see from the site that they linked confirms the "pro-Tesla" person's statements.
Chevy sold over 200K Corvairs each of the three first years of launch.
First 12 months deliveries of Tesla Model 3 were a little over 26K. First 15 months deliveries (which is more apples-to-apples with other company "first year" launches) were a little over 80K.
It's not even close, IMO... Do you see the figures differently?
Tesla has been limited by production of batteries and cars, now they have scaled those a lot. But they aren't the fastest of history, that seems clear. Unless they suddenly sell 125k cars a quarter they won't catch Mustang.