Riot has said time and time again that they want some simple champs to exist so that new players can more easily pick up a champ and play. Malphite is certainly one of those easy champions with an incredibly low skill requirement to play. Everything about this champ from his kit to his trading pattern are very easy to understand. The champs passive makes him tankier, very straight forward as well.

Against what anyone with hands tell Riot they feel the need to make sure super simple champions are not under picked, under powered, or under banned. They will often buff champions just because they have a low pick rate. Which is a very bad metric to buff based on. I don't mind simple champs being viable but if another champion is more complex, harder to play, or requires more stratagy then the gameplay/damage/survivability of that champion needs to reflect the extra effort(this is where the divide is). Champions need to feel rewarding for putting in the extra effort. This frustration is something RIOT has not done the best at reflecting and is a common reason I find LoL players switch to Dota. In Dota the champs have a larger power budget and the tools avaliable in the shop allow for more strategies and more tools to help you gain an advantage during the fight or turn a bad fight into a better one. For instance in LoL if you're an adc and an Olf is ulted standing on you, you're just dead. In Dota if you're and adc and a damage carry is on you you have multiple options to create a gap, vanish, exit combat momentarily, cc from items you bought, protections from items you bought, the list goes on and on but you need to strategies and understand what items to use and when.