I'm hesitant to agree that was Disney's intent as it was obvious after VIII and reinforced after IX that they didn't have a plan for the sequel trilogy.
I agree that they didn’t have a detailed plan, but I also don’t believe that’s inherently a bad thing. I think the intent was always for Rey to be the catalyst for Kylo’s redemption, for example, but I don’t know if they created details on how to get there. So for the major points, I think they had a plan. Those other kinds of details don’t have to be worked out before you even start making something. Truly original movie and TV series (as in, ones that aren’t based on pre-existing material like books) probably rarely have a detailed plan going in. Sometimes, they don’t even have a set plan coming out of an installment. Just as an example, I can think of two situations where The West Wing didn’t. At the end of the first season, when shots were fired at the President and his staff, the writer (Aaron Sorkin) hadn’t decided who had actually gotten hit until they started writing the second season. At the end of the 4th season, when the President’s daughter gets kidnapped, the decision hadn’t been made who would turn out to be responsible. In the second case, the writer had a vague idea in his head, but left the show after that season. The writer who picked up where he left off (John Wells) actually ended up doing something completely different than what Sorkin was thinking about. I don’t think it can be argued that Sorkin, or Wells for that matter, isn’t a good storyteller, but detailed planning wasn’t his thing. Sometimes, you have an overarching plan, but you also see where things take you.
My point is this: the lack of a plan isn’t necessarily the reason for the STs flaws, IMO. They could’ve just as easily had no plan at all and come out with 2 sequels to TFA that were universally loved. So, even though I have a generally positive opinion about all three and the trilogy as a whole, there are definitely spots where they didn’t tell the story they were trying to tell particularly well. And that was more of a problem in RoS than TLJ. This is where the ST falls short of the OT. But the PT, which had all the planning in the world, had the same problem as the ST. Planning doesn’t inherently help.
Also important to note that I’m not saying planning can’t help. The MCU is evidence of that. It’s just not the only effective way to approach this kind of thing.