Make the symbol marker composer make it so you can see what you're making
The symbol marker composer is terrible for complex symbols because you can't see what you're composing until you finish and hit apply, hoping you guessed right about what settings and which component you clicked. See at left below the tiny little representations of the various pieces of the symbol being composed? They're so tiny they might as well not be there. I suggest the vast empty space to the right be used to make the component depictions larger like they were in ArcMap so you can see what you're composing. Or at least give each 'Symbol layer' a unique name so there's some way to tell them apart. The implementation of this is Pro is barely usable if you want to make a symbol consisting of more than a few components. Example below with 10+ components: the different symbol layers all look nearly the same here because they're unalterably tiny.
