Kendra's a cunt but a consistent one, as long as you kiss her ass and don't do anything too stupid she won't randomly kill you. Naya on the other hand is a total nutcase, she can go from being gentle to the MC to murdering him for losing one of her silly games in the span of a few minutes. Even Yakuu wouldn't murder the MC for such a petty reason.
People hold Naya to a higher standard because unlike Kendra they know Naya can be better than that. The same also applies to Orphelith, although imo to an unreasonable degree. She trying to make the best out a crappy situation, if she actually had the power to do something about Homaspernia and Lycalis she would've done so ages ago. Appointing Naya as the guardian of Lycalis was a smoothbrained move though and she absolutely deserves to be dunked on for that.
Naya is a whimsical predator; she does things out of hunger and/or amusement. You meet her when she's hunting, and the only way to survive is getting aroused at the idea of being eaten, which she finds amusimg enough to keep the PC around.
In that game, she makes clear she'll eat the PC if he doesn't make an effort to survive
Naya is wild and chaotic; since Lycalis apparently operates on a might makes right mentality when it comes to leadership, she's the leader for being the strongest. That strength is probably part of the reason she's a Guardian.
Her attitude and personality are also the main source of conflict in her path: the responsibility of her positions clash with her whims and carefree actions, causing problems for her, those around her and even her kingdom.
Perhaps that's one of the changes the PC could cause in the game world: helping Naya improve... or worsen her flaws.
When it comes to Orphelith... well, people are being more unreasonable with that one, in my opinion. Like you said, if changing things were easy, she'd have done it already
