Considering two things: the thread is -2,
You consider AP malphite completely op with no counter, only with ONE ITEM. No champion scales that much unless he got hyper fed, meaning you only have something like 2 doran's rings to his deathfire.
He is by no means, hard to kill. He's full AP, meaning he dies just as easily as any other AP if he goes in at the wrong time.
5 Qs of what champion?
Pretty much every champion with some sort of dash can use DFG before it lands,
And if he built only armor, that means you played an AD assassin or something similar. I'm thinking zed. In other words, you didn't build armor pen first. It seems unsual and some people may consider you dumb, but you can at least hurt the "Unbeatable, super tanky with tons of damage" malphite. And you aren't weak with armor pen, you still do damage. And this build vs a burst mage = him dead in an instant to anyone with a stun or something similar.
If he kills your damage carry instantly, it means you gave him a little too much room to work on. Unless your damage carry was on the front line, Malphite will be very close to your team for him to ult into the back.
Oh, and it is a rage thread. You don't use punctuation or grammar, you call him OP when he built only armor, meaning you didn't have an apc on your team. And from what I read, he does this with 240 AP. Shall I do math?
270 + 144(60% of 240) = 414 magic damage.
220 +83.85(30% armor(89.5 + 190) + 48(20% of 240) =351.85 magic damage
400 +240(100% of AP) = 640 magic damage.
1405.85 magic damage total, *1.2 from DFG's effect(Not counting max health as that's too different on each champion):
1687.02 magic damage.
This is pretty much the same damage as every AP character. So please, don't talk about what you aren't aware of. Malphite is balanced.