Leblanc destroys most of her early lanes, gets a nice spike at 6 and 11, and drops off late game. If your team is full of squishies, sure, she just keeps spiking and spiking and becomes an unstoppable monster, but shame on you and the rest of your team for picking 5 squishies. She isn't a real plausible threat in teamfights if your frontline is even decent at their jobs. She's squishy as all hell and if she unloads her burst on you then your carry gets free rain of her team while she waits for cooldowns, or she has to juke around the tanks to get at the squishy, which sets her easy kill combo (q r w w) on cooldown while her w is down. again, while she's looking for an angle on your squishies she's doing nothing for her team and it's a 4v5 fight.
And if she gets behind and can't even burst a squishy, it's game over for her.
She's mobile, yes, but using her double mobility also removes most of her burst damage, unless your team decided to clump up and get double distortioned. And other champions punish that grouping much harder than LB (Orianna, Malphite, Gnar, Viktor to name a few)
LeBlanc is not overly overbearing, unless you try to get in her face as a squishy.
TL;DR you guys don't realize that her insane burst combo can't be combined with her absurd mobility combo. She has to choose whether to reposition or 1 shot someone squishy, which plenty of other champions can do as well (You don't complain about Syndra's point and click "I hate you, you're dead"or Malzahar's "Okay I'm going to ruin your day no matter how tanky you build" playstyles. LB risks her body for a superior burst, lower CD, and some mobility. I think that that's a fair trade)