There are heroes that are made tank that does nothing to the attacking forces, i.e. Vivica, Ares, Zulag, etc. by reason that their skills involve direct healing or HoT plus other buffs. They are called tile dump tanks. Kunchen, while having tanky stats especially when emblemed, not only heals himself and allies, he renders defense down to the attackers resulting to a much higher regular or skills damage from Kunchen’s defending allies. Most favored are tanks that does not only do some buffs and/or heals allies, but provide status ailments against enemies plus damage, if any. Telluria is one fine example of that kind of tank. Not only she has tanky stats and perfect class for tanking, her heal over time and minions to allies plus the mana regen ailment to enemies and minor initial damage makes her suitable in tanking, especially the original version when released in the live game. Ursena, though not as tanky as Telly, when made as tank, make the player think twice of bringing holy heroes against her because of her reflect while dealing massive AOE damage to all enemy heroes. Black Knight has good tanking stats, gives attack buff to allies while protecting his allies because of his taunt and all incoming damage due to him has a 50% to only deal 1 damage because of his JUST A FLESH WOUND skills.
Level has nothing to do with it. It depends on the raid arena and alliance you are in as they involve the level of players you are regularly raiding and the level of the alliance you are regularly warring with.