My biggest complaint for the story lately was the complete lack of it. The block structure was how the setting and conflict was introduced, the climax, then resolution. Now it's firehosed into our faces and we move to the next world. I assume because WotC is so concerned with making a bad story and being committed to it for 9 months they want to reduce their risk and never build anything monumental.
They have done multi plane stories in the past before that were fine. Masques, Nemesis, and Prophecy were all one different planes and self contained stories that were rather tame but Nemesis is probably one of the best books in the game. Masques sucked, but it had a lot of potential, it's just that they turned it into a Saturday morning cartoon which stripped the story of the otherwise interesting character building the rest of the series had.
I think the bigger problem is that every plane is now just a tourist attraction, because whereas Dominaria, Rath, and Mercadia were all unique worlds with a lot of character and story building modern planes are just Egyptian theme park, 1920's gangster theme park, Greek theme park, etc. That and they try to make every story some great world altering doomsday threat, which just makes it all blend together, whereas Masques was an adventure in a new world, Nemesis was the story of the villains and how their politics worked, and Prophecy was a look at other cultures in the world we already knew. It was all tied together by an overarching threat, but it was much more reserved, in that the threat is there and all of the stories are working against it, but on a more practical level instead of extreme action scenes.
There used to be a single overarching lesson from old-lore too: discipline in progress. Argoth is sunk in a petty squabble, and Phyrexia was unrestricted and amoral progress in technology. Urza, while attempting to destroy the Phyrexian progress he saw as a threat, ultimately reinvented much of it and was tyrannical to the entire planet. It would be a poignant lesson today, with kids glued to screens and having no attention span.
The old lore was really good despite being a franchise series. I think you got it right that it was incredibly disciplined and was willing to present stories that were more reserved in nature. I think it also understood that a good villain is key, because the modern lore uses the names of classic villains in the story but doesn't really give you insight into who they really are besides the basic mustache twirling bad guys, with maybe the exception being Urabrask who seems to be written more like a good guy that happens to be on the baddies team. Whereas the classic lore gave entire books to the bad guys to flush out their stories, whether it was Nemesis where we saw their inner politics, The Thran which explained who Yawgmoth was as an entity, or Bloodlines which gave us a look at the Phyrexians in contrast with a rogue good guy like Garra. Even the book with Xancha (Planeswalker?) was more about Phyrexia and its culture than about Urza directly as it was written through the eyes of a Phyrexian.
They also were great about making it out to not just be good versus evil as many characters on both sides view Urza as being far too similar to Yawgmoth, but each side rationalizes why their cause is better, and even characters like Gix are given some depth to show how they went from freedom fighter for the poor to the incarnation of rape.
