Unless, of course, they don't- in which case comparing them is misguided, and shouldn't be done. That would be a point of contrast instead- recognizing the differences, in intent and effect. None of which have any objective measure about what is better, only about what is different and then a subjective what was enjoyed by individuals.
Comparing entire Bioware games with other entire other RPGs as a one-to-one basis would be silly, which is why most people will pull compare specific elements that are worth putting side to side. A classic Bioware game and a typical Bethesda RPG approach the premise of telling a story and player choice in significantly different ways- measuring them by a single standard would be misleading because they aren't even pursuing the same goal.
Misguided in what way? I've given you plenty of ways to compare them. No, the fact is that around here comparing any BioWare game to anything else is like a sin. I've seen it so many times before that it is ridiculous. Someone tries to compare two games, and it always ends with "they're not comparable because x or y". The fact is that both have similar elements and like I said before I wouldn't compare them through their mechanics, that is pointless, they have different gameplay and thus are not alike in that way. Aside from that, they have a lot in common. Seriously why aren't they comparable? I have heard nothing that supports that, just the same old tired argument, "they don't have this in common, therefore they are not comparable".
As with analogies, no comparison is perfect- it's the degree of imperfection that makes using any standardized measure pointless and more subjective than not. Case in point: the idea of magic. Magic and mage society exists in Dragon Age, the Witcher, and Harry Potter, and all three have some superficial similarities: magic has unique abilities and is unique to a small population which is generally isolated from mundanes and have the potential for disproportionate influence.
But the differences between the presentation and nature of magic in those societies is so different that making comparisons between them to support an argument in one particular setting is meaningless. Magic in the Witcher doesn't have a suitable equivalent to the dangers of abominations, demonic possession, or pure mass destruction that it does in the DA universe: mages are viewed with suspicion, but not a potential existential threat. In Harry Potter, mages and magic are even less threatening. Making comparisons to one setting or another doesn't work well.
And who's claiming any comparison is perfect, I only stated some points on which they could be compared. You're putting things out of perspective, in all those cases there's more than just a simple thing that brings them together, I didn't choose to exemplify them just because.
Interesting you should mention magic, and more interesting that you also mention that the mages are not considered threats, especially since the person behind everything in TW1 was a mage. There are certain monsters that can only come about through magic in the Witcher, You want an equivalent to abominations? There you have it. TW2's plot revolved around mages and some of the biggest threats to the northern kingdoms were perpetuated by mages. Mass destrucion, take a look at act II, you'll see the mass destruction that a sorceress caused both in the present and the past, through both sheer destruction and through a curse. Want a place that considers mages a danger, go to Nilfgaard, talk to Letho you'll see what they think of mages. In fact all the trouble Nilfgaard went through to do what it did is very much indicative of how they view mages.
Claim what you will, whatever. These games have more in common than people around here claim to admit. Trust me, when both of them get released you'll see more than one person comparing them. In fact I'm sure someone is already doing it anyway.