[@Obscene Symphony]
[hider=A breakdown of Drakken/Gem advantages and disadvantages according to my logic]
Depends on your point of view.

I believe someone, you, I think, said that a Drakken around a hundred years old is equal to a twenty-year-old human/Gem. So theoretically, that's not entirely true. Drakken have more time to learn, yes, but they also mature and grow much, much slower than a Gem, meaning that Gems could raise a more dynamic population of skilled soldiers faster and more consistently than Drakken. Gems would technically be smarter, because they could learn much, much faster. 

So elementally- if they are old, they are skilled and undoubtedly better, unless they had that mindset of "I'm going to live for two or three more centuries, why rush with the learning right now?" But a hundred year old Drakken would likely fall prey to Valence and any other elite Cultist.

In other words-
Gems grow and learn faster, so they can become skilled faster, but they also age faster.
However, Drakken age slower and therefore learn slower, but they will be 'skilled' for a much longer time.

Natural selection also plays a part. 

The average Drakken would not be so intelligent and therefore harder to teach and drill; lieutenants and the upper echelon of soldiers would be much more likely to be above-averagely skilled in combat or elementals. The highest echelon- generals and warlords and their direct underlings- would be mainly intelligent in some ways, as well as powerful. The average Drakken soldier would mostly be from soldiers before them, or civilians- thus, the majority of the Drakken won't necessarily have as much strong genes to choose from. 

Meanwhile, the Gems would have a little bit more. While there is still some amount of separation- I doubt the royalty gets much commoner blood and vice versa- the majority of Gem genes are mixed up, without as much segregation between class or element. People marry people freely, for the most part. Thus, the Gems would less likely have an upper echelon of higher genes, and therefore, elemental strength and skill, as well as natural body traits such as being a natural runner, swordsman, etc. 

Accordingly, the average Gem is, in relation to the rest of the Gem race, better than the average Drakken, in relation to the rest of the Drakken race. 

Given the Cult and its goal, however, there would be eyes on many possible candidates for becoming a more skilled warrior in the event of war, as well as families that have been started by Cultists who sought to both have a life and love, and to strengthen some bloodlines. 

So, theoretically speaking, Gems would be a match for Drakken in the long run, and the Cult could be a match for the Drakken invasion in the short run.

I mean, if you're all that determined to defend the Drakkens' superiority, then how is this supposed to play out? How was it meant to play out?

The Gems have:
No sizable or notable army to stand against the Drakken
No significant fortifications anywhere, except for a couple fortresses
No elemental advantage, because Gems have one element and Drakken have two
No skill advantage, apparently, because Gems mature too fast and die too fast, without having the power or the time to refine their single element
No physical advantage, because Gems are smaller, weaker, and likely slower than the larger, faster, stronger Drakken
No political advantage, because the Drakken have such power over the Gems that there is no possible political maneuvering
No tactical advantage, because the Gems have never actually fought a war in their lives, except in dire circumstances
No strategic advantage, because the Drakken are a notably more powerful nation with significantly more resources and experienced
No hope, because they know that the Drakken are very experienced conquerers, and the Gems aren't
No conviction, because they've been protected and relatively babied for years by the Drakken; they didn't need to deal with outside hostiles with the Drakken's protection
No standards, because they've been giving away their daughters- their children- for years, to be married off to a warlord.

The Cult would be the only ones that could change anything in the event of a Drakken invasion- so [i]please[/i] let it go, that the Cultists have just a tiny bit of a skill edge, you know?

The odds are, quite literally, stacked against the Gems. The only advantage the Gems have is that the Drakken are attacking, and the Gems are defending. Except, the Drakken already know where all the cities are, they've crossed into Gem territory plenty of times, so they know how the land goes and likely have maps. 

So the Gems have no advantage whatsoever. 

Well, that's not entirely true. They have the advantage of intelligence, and maybe some espionage/sabotage/assassination. At least, for as long as the Drakken disregard their Brides as a threat.[/hider]