I agree with some of your criticisms of Mortis - it is weird, and not subtle. My main concern re: excluding it or chopping it up is Morai, who appears prominently at the end of the Siege of Mandalore, and also in Rebels. You sort of need to recognise that she’s connected to the Daughter and Ahsoka’s resurrection or she’s just a random bird. That, and the appearance of the Mortis Gods in Rebels, as mentioned previously. I know that you’re not necessarily prioritising things just because they’re interconnected with other stuff, but the Mortis mythology certainly seems like something Filoni intends to develop further in the future. It feels to me like a significant thing that TCW establishes.
Like you say though - nothing stopping anyone from just watching it, or even making their own combined fanedit for the arc in the same style.