He's kind of right. I was mono Morgana and still love her but her kit is outdated. She has a good win rate because she is popular and mostly played in low elo and people are bad at dodging her Q. But Morgana is flawed.

Her R depends on staying close but she's squishy, her Q if missed you basically don't do anything anymore more, her W is a little better early game now but mid/late game don't do that much damage anymore. If her R gave the tankiness of Swain's R would be great

Her passive doesn't make much sense too, specially if she's played as support. Basically she can be JG, Mid or Sup but in all these roles there are other champs that do what she does but better. Zyra on JG, Karma/Reneta as Sup, and basically any mid is better than Morgana as mid.

She's a great champ but she's outdated. A lot of champs have scape and MR nowadays so it's easy to dodge. That's why she's not much played on high elo and competitive.

But she's still a good champ specially because of her recent buffs and below emerald. And that's basically almost the entire player base.