It's nonsense to compare Valeska and Tur-Sar based on the matchup between cavalry and archers. You need to evaluate who is more useful at the start. Obviously, Valeska will often have more archers at the start than any other hero. Since the early game revolves around archers, people choose Valeska (and I'm not even mentioning that ranged attacks are significantly enhanced). That's the whole logic. Tur-Sar has his own advantages; his tactics allow him to easily overcome ranged defenses, and a stack of spearmen is also effective. There's also the hero Orrin, who shouldn't be forgotten. And of course, Caitlin.