Ares is a stronger healer then guin. Most classes are paired with another class with healers for quests. There was a lot of balancing of hero’s to which class on beta so that common hero’s and healers are proportionally mixed to complete these quests.
The only quest that has no healer is barb/rogue and that won’t be for long. Clerics isn’t even that great especially for 4* hero’s where mana manipulation isn’t that common. For instance alby as a Druid is likely better then north as a cleric since it makes alby much more durable.
I’m also not saying guin wasn’t given a strong talent becuase she was already to strong. Guin (or any healer) as a rogue would be incredibly strong.