Rhaast is absolutely unkillable with this build

I just had to play versus one and it was ridiculous. He could outheal damage of 3 carries and kill them with his damage as well. His Q healed him for +420 on both instances. Just crazy. By the end of the match, he had healed 35k and damage taken was 65k (39 minute match). I don't get why people think this champion is UP or something.
Note: Our ADC had
.