The problem is, your borders will increase linearly while the area you have to defend is squarely. (well I don't know if that's the correct way of saying it in english but i hope you'll understand, can't really think of a better way to explain, fail
At first, this might seem like an advantage. But if you're relying on decryption for defence, it is actually a disadvantage. After your empire gets bigger than a certain size, you will not have enough enemies to generate enough decrypted to defend your lands.
To "solve" this issue, you said that you should decrypt every trained unit. With dwagon relay, that is possible to some point. But remember, dwagon relay isn't teleportation. It has it's limits. It is true that those "limits" won't actually matter until your empire becomes very,very,very huge. But eventually, it won't be able to keep-up with the production of your cities. (Which means, you won't be able to decrypt everything that pops) (remember, only one caster can decrypt, and she can't be in every city when they produce something. (we're talking about abnormally big empires here))
Then you have to make a choice:
1)You continue popping units, but since you can't decrypt all of them, you will have to pay upkeep. Which means >> your empire will eventually fail to sustain itself
2)You only pop units your decryption can convert, but this means that you're production is "capped", which also means that you won't be gaining units faster as your empire gets larger. Which also means >> your empire won't be able to grow after a certain point
Why can't you decrypt all of them? What he's suggesting is to execute all
units, harvestable or not, as soon as they popped (or as soon as Wanda gets to them. If this was done in a pocket kingdom, there wouldn't be any need
to expand borders at all.
So, lets suppose GK somehow fooled the initial RCCI expedition into thinking GK's a smoking crater (or a lava lake, or whatever). After that, Jack could keep their one city veiled indefinitely from passing air troops. Let's suppose then they stay undercover for a thousand turns. If all level 5 cities produce at the same rate, over these thousand turns they could pop eight thousand pikers, all of which would be decrypted immediately such that they'd never need upkeep. Now, we don't know how many schmuckers a level five gives you, but what's left over after the casters' upkeep should be in the hundreds of thousands or more range. So after these 1k turns they'd have accumulated millions if not billions
of schmuckers. If all of these schmuckers were used to pop hobgobwins, you can add several thousand of them to the horde.
By now, hopefully everyone's forgotten about the name Gobwin Knob, but even if they haven't it won't matter. The city's defended by thousands upon thousands of units now; a completely unassailable fortress. Then the strike force is sent out on a campaign of slaughter. Drive straight for each capitol in sequence, cleanly severing the heads of the opposition. Once all sides who could possibly remember the location of Gobwin Knob are out of the picture, let the harvest begin. Every unit from each of the now neutral cities are croaked, decrypted, and then added to the horde. All cities are razed, with the schmuckers saved or used for (decryptable) Hobgobwins. Then go back into hiding for another thousand turns, until the nearby area has been repopulated. Rinse and repeat until all regions within easy reach of GK have acquired such a fearsome reputation that nobody would touch them with a ten-hex pole. By this point, your decrypted forces should outnumber any side's living forces by two-to-one to five-to-one. Then begin world conquest. And if you fail, just go back into hiding and try again later.
This can be done even if you can't find a way to execute your own troops besides harvesting; a fleet of a few hundred decrypted dwagons should be able to solve your garrison problem soon enough, since you don't need to defend the land you're taking.
The point I'm trying to make is that there's no known limit to how many decrypted troops a side can stockpile. You could replace the 'raid and hide' plan with just a steady advance, never going so fast that you don't have enough decrypted to fully garrison your cities, and never using decrypted units on the front lines, there's nothing known that could stop that side from achieving critical mass and becoming literally impossible to beat eventually.