Thank you for comment. I totally agree with you. There is no need for domain layer to take advantage of CQRS usage.
Mediator pattern is great upgrade for CQRS application layers but it brings headache for junior developers when they are moving through codebase.
Actully, there is no need to implement mediator by itself. There exists a great nugget package called MediatR, and its so clean and simple, that I fell in love with it.