"No weaknesses"?
Darius has no mobility whatsoever, can be poked to death with impunity, has barely any cc to speak of (his E is barely usable after the nerfes and in total, brings 2 seconds of slow on his kit) and can be kited by anyone who has any idea what they're doing, not to mention having no innate tank steriods.
Garen is still a bit over the top, but is, on average, slow, vulnerable to poke, lacks consistent sustain and will get killed by any form of % of hp damage.
Skarner is an issue, but he's squishy and can be cc'd and killed quite easily. He lacks sustain in the jungle and (ironically) lacks consistent damage.
Mord is the easiest champ to kite in all the league and no matter how nasty his Q is, he STILL won't scale into late game like an ADC will. Be careful early game and he becomes a liability late game.
They do damage BECAUSE they have such clearly defined weaknesses. The only people complaining are the ones who rush in and try to 1v1 them, and then (rightfully) get eaten alive.