Oh the irony of you saying someone has "whiny sour grapes"...
If you honestly can't see the difference between The Empire Strikes Back and Hobbit 2 then I don't know what to say...Empire at least ended the storylines, just made sure you knew more was to come. Luke and Leia on the medship with the rebels, Chewy and Lando on the Falcon going to look for Han...if this had been like Hobbit 2 it would have cut off after Han was frozen in carbonite. But instead they had Luke face Vader, Lando helps Leia and Chewy escape and save Luke.
Look at how Two Towers ended, it too was leading into another movie but found a place to end the flick that made sense. Even though we all knew Helm's Deep was only the beginning of the War of the Ring it was a perfect cutoff point and left the third movie to be about the battle at Gondor and Mordor. I equate the ending of Hobbit 2 with cutting Two Towers off after the one orc blows up the wall. Then the King of Rohan could say "what have they done" and then faded to black.
It isn't about how we know another movie is coming, it is about how they could have added twenty minutes and made the movie a thousand times better. (Or maybe cut down on some of the needless bloat to make roo.). This is all part of the issue with taking a 300 page book and making into a 540 minute movie. If you let your inner fanboy take a break you would see that.