I'm not sure what you mean here... but Scala 2 and Dotty have the same incremental compiler, and their independent bridges feature overall the same quality (which is high and heavily battle tested, for those interested).
The quality of the used names extraction affects accuracy, but not compile speed. I must say, Dotty and Scala are extracting about the same amount of dependencies, with some corner cases being covered better in Dotty (for example, changes in constant values).
I don't see a way Dotty can become a faster incremental compiler that doesn't involve adding the incrementality in the compiler.
Edit: typo