An earthquake can't be evil as it is not a living being... Evil/good depends on your morality and that is something that animals and in this case Daedras do not have. Even in our world there have been moral differences between different societies since the beginning. For example ritualistic cannibalism was practiced by different cultures throughout history yet it wasn't evil to them.
You're using an EXTREMELY moral relativist point of view. It's not very helpful. By that measure a serial killer doesn't do anything evil if he doesn't personally consider it evil. [censored] and the most brutal of slavery wouldn't be evil if the people performing those acts didn't consider them evil. No offense, but it's a worthless perspective, because it essentially is just saying you can't really judge any acts or person in ethical terms. (And no, there's no logical reason why you'd draw the line at societies and not the individual -- and of course an individual's views on morality might change over time, might not be consistent, or might not exist).
If you judge morality based on the results of actions, then an Earthquake can quite easily be evil. If it kills people, and killing people is bad, then it was evil. Same with a plague or anything else. This framework for judging morality doesn't care about whether something is thinking or not in determining the morality of a given event. I find this the most useful way to look at morality.
If you judge something based on the motives or other cognitive processes, then it is true that you can't judge an earthquake as evil. However, daedra DO have motives and thoughts and you could certainly judge them. A daedra obsessed with destruction and misery would be quite fair to call evil. That said, while this also is a very old school of thought, I don't find it that helpful. Determining motives isn't easy, and I feel it really misses something when someone has good motives but is incompetent (and therefore causes great harm) or bad motives and incompetent (managing to do great good) -- the latter is something a results-based perspective can more easily accomodate, imho.
For the sake of clarity, I suppose you'd say that a sociopath isn't good or evil either then, yes?
As for the historical argument. Shall you next argue that we haven't progressed technologically either? We just have different ways of doing things than people 10,000 years ago and they are both just as good? Way to ignore the Zeitgeist.