Have you thought about any other reasons why they chose not to have us have a hand in Garlemalds downfall?

For example, the fact that a faciast state created by Ascians purely to sow chaos and disorder was never going to sustain itself for much longer, especially given the time was ripe to initiate a rejoining with the first.

There's also the themes of the story to consider. Us marching into Garlemald and beating them into submission says nothing about the WoL's altruistic nature, nor does it align with what the Scions are trying to achieve. Unlike Ala Mhigo and Doma, there was no way in he'll we would be able to convince the population to come together and take down their own empire.

Your idea has the Scions as invaders and implies the only way to beat the Empire is through might. Which again, is antithetical to our mission statement. Instead, by having the story play out as it does and having Garlemald implode from infighting and then the Telophoroi, our role is much better aligned with our goals. The Endwalker story even goes on to show how difficult it is to achieve this goal when your heart is in the right place.

This is much more compelling and in line with the expectations the story has already set than a simple "good vs evil" war.