Both tools are pretty awful. They are primarily meant for debugging (there is much more efficient and convenient ways to do import/export data), but their output manage to be hard to handle both for humans and for tools (especially as soon as you have modern stuff like composites).
There is value to having tools to export sstable contents into a format that is easy to manipulate by human and tools for debugging, small hacks and general tinkering, but sstable2json and json2sstable are not that.
So I propose that we deprecate those tools and consider writing better replacements. It shouldn't be too hard to come up with an output format that is more aware of modern concepts like composites, UDTs, ....