No, it's consistent with the whole premise (and builds the story of evil being able to resurface, because after a long period of peace we grow complacent - which is absolutely, 100% true). Rather, it would be difficult to believe that a random bunch of elves in the middle of nowhere is vigilant to some unknow threat, while their own king is calling off guards around the world because he believes they serve no purpose anymore. The example comes from the top.
It doesn't undermine Arondir at all. There are always individuals who think differently - and Arondir is one of them - but most just follows suit. It's absolutely natural and believable. That's what makes Arondir special, contraty to most other "people" or "elves". That's what makes him a protagonist and not just another elf. Nothing's contrived here, it all makes sence in the story.
As for Adar - there's no reason to speculate. We will find out.