The S4 finale of "The Umbrella Academy" made me feel as if I had just done a month long hike up a really big mountain, and as I reached the peak, waiting to see the world spread before me in a glorious panoramic view, yet I was met with nothing but fog. The disappointment was, as you imagine, visceral.
I think my biggest issue is that they did what a lot of shows do when they're lazy... Invent time-skips that "resolve" a lot of previous issues that they do not have the time or the writing capacity to deal with. Humans are dynamic. They do not just resolve things and move on. They will come back to traumatic events from the past, and they will have lingering thoughts about them even decades into the future. This idea that a time skip can change these people (I know that they are characters, but is that not why we consume media? To "know" character but "see" and "feel" person on the screen?) so inherently that all of a sudden certain things are magically resolved, is idiotic. Personally, I find that "Yellowjackets" and "House of the Dragon" are a masterclass in time skips done right when it comes to the complexity of character psyche.
I clearly have a plethora of other issues to go along with it like weird and clanky temporal and spatial allocation (did someone say "Shadow and Bone" S2, what is going on Netflix?) where you cannot discern how much time has passed or how long does it take the characters to travel from point A to point B. The million and one questions that needed actual answers and the decision to introduce MORE elements (i.e., Jennifer and the Squid) that would just remain unanswered. Like, it's one thing not to answer the questions viewers have had from S1, it's another to add more bullshit into that mix. Lastly, the characterization and the utterly unhappy ending of it all... The they-were-meant-to-die-all-along schtick is so outdated. Is it fitting? Maybe, sure... If the narrative was constructed to guide us in this direction, but it never was! Not even in S4 itself!
If you want to pin the "blame" on someone for the Marigold and Durango mess, it should have been Abigail, and with a few tweaks to her inconsistent characterization, it could make sense. She should have been the one to absorb the children's Marigold out of her own repentant volition (if she really wanted to fix Reginald's transgressions INCLUDING traumatizing a bunch of children for his own selfish agenda), with Viktor's help (because why have him be able to give and take away Marigold FOR IT TO NOT HAVE USE WHEN IT MATTERS MOST???) and then she should have sacrificed herself to the cleanse, killing Ben with her and reclaiming the original timeline. Yes, yes, Ben dying is very unfortunate, but I think it is thematically beautiful to see how his initial death broke the family, and how this one unites and potentially heals them. It would also mean that the guilt does not remain at the hands of the abused children, but instead, a parent figure rises up to the task and assumes the role of responsible parent, something that Reginald was incapable of doing. I also think Reginald should have succumbed to the cleanse after Abigail's sacrifice (suicide, yet again), which would mean that this is the closest they get to the OG 2019 timeline: Reginald, Abigail, and Ben are dead.