Kylo's turn to the Dark Side was all driven by Snoke. It was all a manipulation by a Dark Side master. Snoke sensed Ben's raw power and used the family connection to Vader in order to pull Kylo's strings the whole way. He made Kylo want to continue his grandfather's unfinished legacy. That's why some of the Kylo/Snoke interactions end up referencing Vader so often. Snoke keeps invoking Vader to keep manipulating Kylo into sinking deeper into the Dark Side (to prove that he's worthy of inheriting his grandfather's legacy). Snoke keeps making Kylo seem like a failure just to keep building up his anger. But Snoke created a monster that he couldn't tame.
When Kylo kills Snoke, he cuts the puppet strings. He's in charge of his own decisions and motivations now. That's the intrigue for the Kylo character heading into Episode IX: is he really Kylo Ren? Or is he really Ben Solo? Did Snoke's manipulations change him permanently? Or, now that the puppet strings have been cut, will Ben Solo be reawakened? Snoke's death was the key to setting up that part of the last chapter. So Snoke's death wasn't a waste at all, the way I see it. It was necessary. Kylo is now set up to determine how the Vader/Skywalker legacy will be defined.
No one wishes Snoke had been on screen more in TLJ than I do; trust me on that! But the story here is not about Snoke. He was a key device to drive the ST plot, but not a central character in terms of the Skywalker Saga. The story needed to shift (leading to Episode IX) more toward Kylo, who is the only actual Skywalker among the new crew (that we know of). Snoke's death served that purpose really well, imo.
And I've heard/read this same sort of analysis of Poe countless times, and I just fundamentally disagree with it. At the end of the movie, Poe is the one who takes charge in leading them out of the bunker; and Leia even tells everyone: "What are you looking at me for? Follow him." To me, that was the punctuation point for Poe's TLJ arc. He's becoming the next leader of the Resistance. The learning process for his character throughout the film was about realizing what it takes to do it most effectively. I don't see how all that stuff fits with some "anti-masculinity message" behind the Poe characterization.