I think what hurts the adoption of Dart most are articles like these which advise to stay away from it.
The language itself is really good and nice to work with, the libraries are well designed and quite feature-complete and theres a good amount of tooling available.
Regarding the server (or general application development) comparison: I think the real opponent is node and not Go, because both use a singlethreaded model with lots of async functionalities (callbacks, futures). For some types of applications this is much easier than handling real threads/goroutines, for others you might want real parallelism.
The language itself is really good and nice to work with, the libraries are well designed and quite feature-complete and theres a good amount of tooling available.
Regarding the server (or general application development) comparison: I think the real opponent is node and not Go, because both use a singlethreaded model with lots of async functionalities (callbacks, futures). For some types of applications this is much easier than handling real threads/goroutines, for others you might want real parallelism.