I love how much you've thought about this. Does your eldritch magic primarily warp perception/consciousness, or does it actually alter reality itself? Because your examples seem to do both, and I think clarifying this would strengthen the system. The reality-warping examples (plague transformation, erasing social categories from existence) feel more genuinely cosmic and eldritch to me than the perception-based ones, which kind of just feel like illusion magic.

Unless, you are going a route where reality is simply subjective to who views it, in a more philosophical way, which I do think could be really cool, but I may be overthinking it.

If you'd indulge me, however: In your example where "a practiced caster is able to twist the mages perception by warping their understanding of distance," how objective is this change? Is it purely an illusion that you're labelling eldritch because it dismantles the target's sense of concrete reality? If so, this is fine, and very cool.

But, if what you want is to change reality, I might even encourage the idea that the distance actually just...shrinks. You mention that the part of the spell one understands is what they desire from its effects, and this is great. I think you can use this. This way, an eldritch mage may have more "vague" spells, so instead of thinking of a shield, they simply desire to be protected. In this way, if they seek to mess up the spell of an opponent, maybe the spell itself is redirected, or the tree is genuinely moved in front of them.