Look, I'm not saying the Ancients were weak. They were quite powerful to have conquered as much as they did (Knossos portals were one of their greatest achievements as far as we know). The reason they lost, however, was because they weren't used to adapting quickly (something which only happens when you encounter difficult challenges, i.e. fighting an entrenched war for a long time). They did discover how to destroy the Lucifer, which is quite a feat for a race to accomplish, it was just too late to carry out. Now, if the Ancients were used to adapting and advanced technologically as quickly as the GTA & PVN, they could have been able to destroy the Lucifer before it wiped them out.