I can’t see what the problem is here. I’ve been using FCP since v.1 and never ever found this dissolve issue difficult to wrap my head around. If you don’t have the media, you can’t make a dissolve = simple.
Maybe iMovie is a better alternative for this kind of stuff? Personally, if I use a dissolve at all, I prefer keyframing b/c the stock dissolves are never pretty IMO.
I think if you’re missing the point of how the dissolve works, you’re probably missing a lot of how FCP works.
Why fight it?