I've seen many people claim that tsunderes, or a specific tsundere character (mostly Kirino, Asuka, Haruhi, in short, popular ones) to be dominant. Is that really so?
I personally consider dominant a girl who is clearly leading in the relationship and enjoys it (Pushing down the guy to kiss him, for example), while tsunderes just want the guy to lead and when he's indecisive, get angry at that. But they don't want to do stuff to him, they want him to go first. That's not dominant. At least, I see it that way.
I do not think that all tsundere are all S. What I think, is that a typical tsundere is just a girl trying to become dominant in superficial sense but fails to do so, because inside she really wanted the guy be the dominant one.This conflict makes the tsundere inflict pain to her partner out of anger and jealousy but not pleasure to show that she is dominant.
I think yandere are closer to be sadistic than tsundere.
That's a very good definition of tsundere, thanks. There are some which seem to enjoy beating up the guy a little too much (Louise, anyone?), but in general for most is anger/anxiety/jealoust/what have you, and not actual dominance.
Yandere... It's hard to say. Most yandere are overly devoted to the guy, and only leash out against those that attempt to "take" him from her. I suppose they could be sadistic in a way, but not in the usual "femdom" manner we normally use.