Regarding Riombara being 'complacent':
During the end of the invasion the Temple of Light in Riombara did destroy at least 60000 CS of monsters...more probably closer to 90000. These would have in large part otherwise be thrown against Enweil. Without the temple Riombara would surely have been destroyed. Note also that Riombara went to war against the monsters for the second time /before/ we had an inkling that the third temple of light would be constructed in Grehk.
It would be good to see these facts being taken into account before Riombara is labeled as 'complacent'...grin. If we would have been more complacent I think that Enweil would have had considerable larger troubles towards the end of the invasion.
Think of it from Enweil's PoV. The monsters declare war on the SE, don't really bother Enweil much at first. Then they come to "test" us, and we kill one of theirs, much to their displeasure. Since we can't get the SE to actually sign peace with us in order to coordinate any cooperation (not that we had much sympathy at the time for your two realms), we contended ourselves with telling the monsters to "stay out of our turf" while we bid our time and prepared. Then, out of the blues, they attack us with full force, and start making demands.
Enweilian pride kicks in. "They dare launch a sneak attack and then ask us, the continent's superpower, to serve them? I think not!" If any realm could make a dent in their war machine, Enweilians were convinced they'd get the glory of it. And we couldn't stand dropping from continental superpower to vassal state in one fell swoop. So we declared all-out war on the monsters, and marched our forces against them. Our armies got slaughtered in an ambush, and many nobles, some very prominent, were killed in the battle. The monsters demand submission again. Enweilians know what it would mean, though, and were both not willing to turn on Avalon and Bara'Khur, and were much too prideful to submit to threats, even by invaders.
So we turned for help. We sought to improve relations and coordination with Riombara, with much greater interest than at first. We got an alliance with the Daimons in order to use their might to get some payback. We suffer massive losses, but the thirst for revenge fuels us against the stronger foe, the comfort of daimonic backing crystallizes our determination. But as we strike serious blows against the monsters, and push them back on many occasions, we turn to the realm at the beasts' core and see it doing nothing. Not only that, but we see that its council is paralyzed by people wanting Riombara to ally the monsters and use them against us, to actually march their army against us. And then a bunch of Riombaran dukes and lords seceded to form a realm with the sole purpose of fueling the monsters' war against us. And Riombara sits by and does nothing, even when the monster sympathizers are gone.
By the time Rio declares it'll do something, the invasion draws near its end. But even after the declaration, they don't actually send troops. They just let the Servants flash their death ray. Enweilians lost a great number of greatly valued nobles fighting the monsters, and while we continue to struggle, we see Riombara just sitting there letting the Light, which we greatly distrusted, zap away at nearby monsters.
Then, when the invasion ends, we get hit by a second invasion, of undead this time. By the looks of the stats, Enweil is hit severely, while Riombara not so much in comparison. Instead of helping, we see Riombara expanding, and even taking a city that was previously ours, and that we had lost because of the monsters, as happened with others.
From Enweil's POV, Riombara did too little, too late, and even that too little was mostly letting others do their thing while sitting back itself. The monster servants seem to have the re-integrated Riombara, who took advantage of the situation to take away for good yet another city of ours (Ete being blighted). We fought Riombara a lot, so we knew what she was capable of. But when the invasion struck, we only saw that in regards to defending DoA, and never afterwards.