Keeping a gonyosoma in a terrestrial setup would be just as cruel. Gonyosoma should be kept as a purely arboreal species with lots of branches and foliage, etc. They are much more active that a GTP and make much better use of an arboreal environment.
We use the term ratsnake too loosely. Spilotes are a world apart from pantherophis who are a world apart from many old world elaphe which bear little in common with gonyosoma which have different needs than coelognathus.. They are all referred to as ratsnakes, yet they are very different animals with unique husbandry requirements. What applies to one, does not necessarily apply to another.