Many years ago, a mechanic at a local bike shop I frequented talked me int a set of Park cable cutters. One of the best investments I made in bicycle tools. Up until them I used a pair of side cutters for all my bike cables and always have frayed cable ends. Unlike side cutters, these have a "V" on both cutting blades that the cable sits in. When you cut, the cable end has a nice clean cut. The tool still does a great job, even 20+ years later!
That won’t have any bearing on the gunk inside the housing, but it will help, operative word is "help", control the frayed end problem. I’ve also become a regular used of a dab of superglue on the cable end just ABOVE where I’m going to cut to help control unraveling.
The gunk issue is something different. It is real and a coated housing helps. I don;t kow what my bike has now, but when the time comes, I will replace everything with coated housings at that time.