That's no true at all. The syntax is pretty similar with few key differences. The idea is for dotty to become Scala 3.0. But, in the meantime, the next Scala 2.* versions will pave the way for 3.0. Meaning to avoid too many breaking changes in 3.0.
The above has been said repeatedly by Martin Odersky (creator of Scala) and the folks on the Scala compiler team in talks and discussions.
Martin has made no guarantee of compatibility or even to supply a Scalafix app. The fact you can do this relatively easily today is just a consequence of Dotty being very young. As it evolves and becomes more complex, there is no guarantee that a translation from Scala to Dotty will even be possible to achieve automatically.
> Martin has made no guarantee of compatibility or even to supply a Scalafix app
The entire point of scalafix[1](developed by the Scala Center) is to bridge the gap between Scala 2.x and Scala 3/Dotty. Martin talks about it in every Dotty presentation.
Just like Go has "gofix", Scala will have "Scalafix", that will automate migration between Scala 2.x (scalac) and Scala 3.x (Dotty)