I actually think that any alternative-Alex in Umiak hands would find reasons stacking against tehe Umiak about as fast, likely even faster.
If you overtax your economy, sometime it WILL break down.
We simply don't know how close they are to that point, nor if they are struggling with rebelious "client states", or if their internal hierarchy is prone to coups, and therefore inherently instable.
Ant hives only work well, because the workers and guards are DUMB.
Yes, they work relentlessly for the greater good of the hive, but all on instinct.
And also only because they're all siblings/clones of each other.
They cannot come up with innovative ways to improve life within the hive.
Therefore they are a very stagnant society.
Furthermore, often ant hives are fiercly competitive, constantly verging war with each other, over food sources, best shelters, ....
And with the Umiak it also seems like they're able to adapt technology, and even make improvements to the technology they adapted to their use, but so far I've seen no indication in the insider that they're able to really innovate technology themselves.
Which is also an indication for a stagnant society.
Sooner or later they will hit road-blocks.
But due to sheer numbers, they might be able to hold on to power in their sector for quite a long while, which will also mean suppressing technology to prevent others from winning the tech-race...
[edit: spoilered due to mere speculation, imposing perceived Earth-norms on Aliens, which may result in completely false assumptions regarding the Aliens]
If such is the case, then the umiak might get serious troubles if a hive along the border breaks down...
But this is all speculation, and may comprise a severe, and dangerous, case of antropomorphisation.