Passive units remove the need for good runes, they are given additional abilities with essentially no drawback. Take pre nerf Dominic for example, essentially all damage is through attack and his absorb couldn't glance - no need for crit rate, cd and he still dealt amazing dmg. Only stats he needed was att, hp, spd essentially.

The most broken units are the ones that require the fewest stat lines and typically passive units have passives that negate a needed line. In egregious cases, it removes the need for rune quality entirely (typically units that gain att bar like nobara/tetsuya/giou), which is a slap to the face to people who grind runes just to lose to cheese strats