As meme heavy as it is, it's laced in truth.
Arsene has a series of flaws where he's actually an early game Persona and nothing else. He learns only a couple of new moves once you start leveling him, and needs to heavily rely on customzation, tweaking, and overall heavy investment to make him good.
His weakness issue gets resolved once you slam him in isolation, but it takes up a few extra skill slots just to subvert that, leaving him with less options overall due to it.
This did not stop me from making him a complete monster with Maeigaon, backed up with Megidolaon in case something was curse resist, but it took me till end game to even do that, and I couldn't use him during the crafting time as he was entirely too weak to even be viable in a fight during this time.