I agree with Terradon and Skinks doing roughly the same shooting for their points under buffs. It is part of why I like have Terradons. The objective holding is also an important consideration. Parting Shoot is where the Skinks pull ahead in straight damage. Terradons in my experience are better at dealing with heroes, monsters, and linchpin support units. Deployment and list make a huge difference in whether or not Terradons are an effective threat. The list I have liked them the most in so far is the FoS list with 20x Chameleon Skinks, 40x Skinks, and two units of 6x Terradons. If allowed, this list is capable of getting all those units in your opponents face turn one. And the presence of a Terradon Cheif makes for a very fast hero to pass out Parting Shoot to both the Chameleons and Skinks while still being able to LoSaT the regular Skinks if desired. And, due to standard Kroak apparatus in the list, it is happy to go first or second in turn one. Depending on the enemy composition I find that I am able to depoly in such a way as to dare my opponent's to either give me first turn or second turn depending on my own preference. In short, Terradons' threat range and the ability to all in with the list adds a lot of flexibility. I am not certain how much better over all Skink vs Terradons are, but I do get a lot of value out my Terradons in the current iteration of this list. Enemy shooting feels like the biggest threat to Seraphon in general. The list I built is specifically to help vs enemy shooting. It is a huge reason I really like Chameleon as well. Behing able to deploy Chams off table keeps them safe until the time is right. The list's ability to alpha strike makes the choice between taking turn or two turn much more difficult for brittle shooting armies like Tzeentch, CoS, and possibly LRL.