Memento was literally a mystery film, and unless you kind of know which context clues to look for you're not really going to figure out what's going on until the end. Inception had a lot of mystery to it in terms of what's real and what's not, but in the end the mysterious portion of it is not really the point of the movie. We're not really presented with the question of what's real as the core mystery to be solved. The fact that Nolan doesn't actually reveal anything at the end aside from the context clues mentioned in the video and in the article posted at the top of the comments and his remarks after that "it doesn't really matter whether or not Cobb is in a dream" lead me to believe a lot of it is more of a character study of that man rather than an overarching sci-fi type world. The journey is not really to decide whether or not Cobb is living in the dream world but more so whether he is at peace either way.
I do agree with your general assertion that Momento is a more coherent film and I think that is largely due to the scope and scale of those respective films' budgets.
On one level, yes. But Memento is a philosophical inquiry as much as it's a literal mystery.
"his remarks after that "it doesn't really matter whether or not Cobb is in a dream" lead me to believe a lot of it is more of a character study"
I think the same point is generally true about Memento.
[Massive spoiler alert for anyone who hasn't seen Memento and might be curious]
The "big reveal" in Memento isn't so much the unraveling of the mystery. It's that the mystery itself is a red herring. Leonard chooses his own reality, regardless of whether or not it's the factual truth, and regardless of whether or not he's caught in an infinite loop of his own creation. The same can be said of Cobb's choice at the end of Inception, running out to embrace his kids (and this particular version of reality) without checking on the spinning top. At the conclusion of both films, the protagonists basically surrender to subjectivity. They realize, consciously or not, that it's the only rational choice they have. They can never know the real truth, so they construct or embrace the truth that suits their needs.
This is what I meant when I said that both films are explorations of the same theme. That theme is basically our agency and choice in the subjectivity of our reality. It's about how we create the worlds we inhabit, literally (in the case of Cobb's "architecture" of dreams) or figuratively (in the case of Cobb's and Leonard's choices w/r/t reality).
Just imagine someone makes a new movie where Lenny, Cobb and Neo are merged into one character in/out of a matrix, a dream and a story with a loss of hippocampal LTP.
I do agree with your general assertion that Momento is a more coherent film and I think that is largely due to the scope and scale of those respective films' budgets.