Comics almost always get streamlined when adapted into live-action feature films; details and plot points get changed or glossed over because not everything from the source material can be carried over to the big screen. The story has to be simplified so that casual watchers will have an easy time following it because there's only so much you can show in an hour-something or two-hour-long movie. The Netflix series here is essentially a feature film that got broken into five episodes, or parts. A second season was never guaranteed, so you have to ask yourself if it's better to only adapt the early parts of the series and hope that a continuation will be green-lit or if it's better to mainly cover the most iconic moments of the series in case there won't be another chance to show them. If you ask me, though, yeah, they should have just adapted the Spirit Detective and Saint Beasts arcs.
The first episode would have Yusuke dying, coming back to life, and becoming a Spirit Detective. The second episode would have him meeting Kurama and fighting Gouki and Hiei. The third episode would have him fighting Rando and being chosen as Genkai's disciple. The fourth and fifth episodes would adapt the Saint Beasts arc; Kurama fights Genbu, Kuwabara fights Byakku, Hiei fights Seiryu and the finale would be Yusuke fighting Suzaku. That's the best way for the Netflix adaptation to go without feeling too cramped or rushed. I get that they wanted to adapt the most iconic moments of the series, but you kind of defeat the purpose of doing that when you're just cramming everything into just five episodes as that doesn't do the source material much justice. Another season would be more likely to get green-lit if the first one is successful. And even if it doesn't come out, as long as the first season is a quality product that adapts the source material faithfully enough, fans and critics will be satisfied.
The showrunners just opened themselves up to a ton of criticism from fans for cramming a bunch of things into five episodes. Whereas if those episodes only focused on the earlier arcs, no one would be criticizing them as long as they're well-made, faithful adaptations of the manga. People would be disappointed if a second season adapting the iconic Dark Tournament never came out, but they wouldn't take issue with the first season itself. Any disappointment over the lack of a follow-up would be a testament to how well-received the first season covering the earlier arcs was, meaning the showrunners would have done a good job. I don't see why there wouldn't be another season if the first one was successful, anyway. This is just yet another example of corporate greed ruining another comic book adaptation.