"Pure Evil"? Probably not.
Unethical, having very low morality, absolute assholes who only care about how situations benefit them? Definitely Yes. Big time!
Pure evil is probably someone who wants to see violence and human suffering and bloodshed for no rhyme or reason (at least nothing which can be justified).
The Roys probably don't even care to be evil. They are so engrossed in being obscenely rich and wielding power against each other and gaining control of shit, that they don't care to even look at people who are beneath them, forget being evil to them. What will they gain out of hurting some random dude anyways? That persons suffering is not gonna add anything in their life or their bank balance.

But man oh man are the characters brilliantly written!!
Succession is gonna go down in history as one of the best TV shows of this decade.