While the final season and overall ending of Stranger Things isn't without its (glaring) flaws, and even though it's probably a good excuse I suppose, I think it kind of works well with the 80's vibe, entertainment in the 80's often had abrupt endings where everything worked out even though it really made no sense if you scratched the paint a bit. They wrote the end to be mostly a happy ending for everyone even though realistically most of the characters should have taken a trip to prison for several decades but who wants to see that?
I wonder how intended some of the parallels with Stephen King's IT were : the first season gives huge IT : Part 1 vibes with all those young kids going around against a monster and the adults being mostly useless of course, but the last season having the grown kids going against a cosmic spider monster was another huge parallel to me, and it was quite satisfying to see for that reason alone (even with the kids teleporting up the cliff).
One thing's for sure, even with a flawed ending, Stranger Things' ending felt a LOT more satisfying than Game of Thrones' ending. Game of Thrones not only managed to create a terrible ending with a really bad last season, it also somehow managed to turn Game of Thrones from "that thing every single person is talking about at the water cooler" to "that thing no one will ever mention again". Have you heard anyone saying they're rewatching Game of Thrones?
I'd even argue that the show ended so badly that it killed a LOT of potential interest in the books, something not even Wheel of Time's adaptation or Rings of Power managed to do.