I
ill have to do look deep but my initial review of the Goodman one….SIGNIFICANTLY better.
1) it’s only CR 13 yet does much much much more damage overall.
2) the regen is a much bigger deal. Not only is it stronger (and again for just a cr 13), but the criteria to remove it is harder. A party that is uninformed about Zargon might not even know what to do, and if they do it takes a characters action to remove the horn (and required a very difficult opposed strength check). So at worst you spend a turn doing nothing, at best it still took out the action of likely the strongest character in the party for one round…which is still a big win.
There is no comparison, Goodman is far scarier for its CR than the OG version