OIALT was Carbdis' first game right? I'd view it as his skills developing over time then, especially if you're comparing it to Eternum. You can even see his skills develop in OIALT. The lighting changes, the scenes get longer and better, environments become more unique, etc, etc. Especially the scenes and lighting.
Eternum was made using everything he's learned from OIALT. And from what little I've played of Eternum so far, he's learned a LOT (Eternum's been pretty good so far, definitely an improvement)