Why do people think Morgana is useless? (I'm in June so please no spoilers)

(If the answer for my question is a spoiler of smth that happens later in the game then please don't tell me, but I've already been told that morgana abandons the PT at some point but I don't know anything other than that).

I've always heard before playing this game that Morgana is the worst persona character ever. I've heard people saying that he's annoying, arrogant, and apparently "useless" too, but I don't understand that.

I just beat Madarame's palace and made him confess. For me, until now, Morgana has been the most useful member of the phantom thieves. He's the one that gives all the information about the Metaverse. It was him who had the idea of opening the door at Madarame's house so that we could proceed on the palace.

Sure, he insults Ryoji all the time, but if it wasn't for Morgana, the phantom thieves wouldn't even exist. He guided the team with all his knowledge about the Metaverse and helped with other stuff, too.

Heck, he even helps you to respond to questions during classes. Why would someone even call him useless?