There’s many ways to skin a cat as they say, especially in SU. I threw that one in as an obtuse option, but like I said, I would not do it that way. Solid tools is preferable for those that have it, or else using the intersect.
As you rightly say, with the tapered top it would be possible if the cutting component were likewise tapered. But note, what I did was have two components making up the full pulley ( so they were a mirror of each other.) so the cutting component would have its taper on the outer face, but in what would be the center it is flat, so where the two meet in the middle would connect to produce continuous geometry - hence the solid inspector returning “nice and shiny”
The later modification is not a Sketchup strong suit. Sub D and Profile builder have some amount of retro active control but it usually requires a “start over”. With some forethought, saving a model at various key junctures will allow you to go back certain steps before a single model is overly modified. Fredo’s new round corner has this as an option now, which is great. Modifiers like Blender uses are also a nice way to allow for later changes before baking in that geometry…