Dont you just love it when a champ meant to be played as a tank is able to build full AP, press R and instantly delete your carry with an ult thats on a 30 second cooldown? Above all else, AP malphite is one of the most unfun things you can possibly play against because all he has to do is press R and win the game. He has a point and click slow to make it easy to press R and win, and since he built ap, that slow also does a ton of damage to. Its like playing against a late game veigar in the mid game, and instead of having 2 skill shots and a cage, there are no skill shots, hes tanky, and he doesnt even have to get you low for the ult to do major damage, he can just ult in, take away all or at least 75% HP, and just clap to kill you, it wouldnt be so bad if this was single target, but its not, its AOE, so unless your tank, if you have one that is, bodyblocks and dies in your place, then you get clapped and your screen becomes grey like an old horror movie, because leagues balancing team is terrifying.
Easy way to fix this would be to lower the AP ratio on the ult, or give it a longer CD, or both, but since they are trying to buff Malphite, reducing the AP ratio would probably be best.