1) I wouldn't put the Elemental Lords on here at all. There are only six of them, they possess wildly different biologies, and one of them was originally a Skrall, which moves it over to the third branch of the cladogram. Anyway, I don't think they'd count as a "species".
2) Also, I agree with some of the previous posters that the two kinds of Vorox and Zesk should be considered the same.
3) What makes you think they all come from an "Original Sapient Species"? Although the Skrall are confirmed to be related to the Glatoriagori, that doesn't necessarily mean they're that closely related. They could have easily evolved sapience separately, especially when you contrast their almost eusocial society with the Glatoriagori's.
4) I'd put the Glatorian and the Agori as much, much more closely related than you have them here. More closely related to each other than to the rest. There doesn't seem to be much of a difference between them besides size -- in fact, I'd put them in the same genus.
5) The Vorox/Zesk should be only distantly related to the others. I mean, they're arthropods, and everybody else is a primatoid of some sort. Again, developed sapience separately.
1. Yeah, I wasn't too sure what to do with them, I just sorta but them there, but you're right they'd actually come from the Skrall, Vorox, and Glatorian.
2. I addressed this in the new tree, I'll have it up probably tomorrow.
3. I just sort of traced back all species and then concluded that the they come from a same species, it's simply a part of my theory
4. They are closely related in my mind, this just shows how all the other species came from them. If you'd like to draw it, I'd be happy to take a look!
5. True, but they have been relatively recently altered, and besides, they are really close to their respective species father-species.
Also, on a side note, this is more of a phylogenic tree, rather than a cladogram.
Some notes on these points.
1) I would definitely keep the Element Lords. It's best to make such charts as detailed as possible, not assume people will already know the more trivial things.
3) The close similarity of the faces of the two major types, Glatorian and Agori, plus confirmed relations between some other groups, and the common way of referring to the whole planet's population as "Agori" provide strong evidence that there was an Original species, and I think it was called Agori.
BTW, the name logic for Glatorian makes sense in that context, as they're named for the gladiator sport they are good at which was invented to resolve conflicts. Not sure if this reasoning works far enough back in time; was that system established after the Core War and were they called Glatorian already? Still, the basic idea at least seems to make sense to me that after a while a trait of giantism (healthy type, or perhaps kept healthy by the cybernetic implants?) developed in some Agori, and they were pushed to the front of the line in terms of who is used for combat.
In the case of the Skrall the giantism apparently continued more than in most, creating the Giant Skrall (ruler class), but for whatever reason they went extinct later except for Tuma. Could be health reasons, as giants in real life often die younger than smaller beings, both in humans and animals. Or could simply be that they wiped each other out in personal duel type battles or the like, as often happens with the strongest and healthiest in warlike cultures, leaving a remnant of only the weak.
I could add other plausibility remarks here but they would tread too closely into controversial real-life subjects, and this is fiction anyways so anything's possible here really. Suffice to say, the basic tree arrangement here does make sense, of the three big families.
4) I don't see how you could plausibly arrange the list so the most numerous tall species is more closely related to the most numerous small species than they are to their respective tall and short cousins. Logically all the smaller types are more closely related to Agori and the tallers to Glatorian. The alternatives are possible but you'd have to add a bunch of evidenceless coincidental subspeculations to it.
5) This one brings up some interesting questions and may throw a wrench in the small/large family branches. That is, why would the same intelligence decay happen in the Sand type of both the Glatorian and Agori?
However, it's possible such a thing could be caused by a virus that attaches to that elemental type. We've seen a similar virus with the Iron Tribe, so it's possible. But even if it's just coincidence, you'd have to have a coincidence anyways if you put them as a fourth family branch; why did both tall and short happen to develop there too, just as with the others? So in terms of story evidence it really doesn't matter either way. So it's probably wisest to stick to the general trend and group large with large, etc.