The logistics are a huge stumbling block for his ambitions, to be sure. Tural is kind of just barely unified in the first place, as we see with the various factions we meet in DT that just plain don't like each other. Prior to DT it is a weak and largely artificial nation held together exclusively by Gulool Ja Ja's charisma and fame vs generations of traditional infighting.

But, giving Zoraal Ja the benefit of the doubt that he could even get his fledgling forces over to Ilsabard, Garlemald more or less is not a functional nation itself and would genuinely be easy pickings. It no longer has a standing army of any notable size and what is left is fragmented without a central command structure. It has a weakened and shrunk population governed by cowardly bureacrats who barely do anything besides consume air and food. Tural could then maybe parlay the few solid resources they'd gain from this endeavor (Cereuleum and leftover magitek) to maybe do something. Possibly. If he's lucky and doesn't just freeze to death. After all, even the Eorzeans struggled to survive against the elements alone with the foreknowledge of just how bad the climate is up there.

There's very little gain for Tural and a high degree of risk. I'm not sure his "we need to teach the new generation how bad war is" schtick he spouts early in the expansion really serves as a strong enough justification for what is ultimately a really bad bet.