I think we have a misunderstanding here, because for the most part you don't get that from the movies either... dooku, Ponda, Baba, Anakin... but not much else.
I guess maybe I was/am used to what was represented in the Clone Wars where you still had a brightly glowing cut in the said opponents armor.
Sometimes death occurring off screen may be appropriate IF the death is particularly brutal... what we assumed happened to 7th Sister. But when MOST deaths are occurring off screen or you are to assume the person died. It makes the death a lot less concrete. Like I said earlier... Darth Maul was brought back in a way I wouldn't have thought possible given how he died and where he was struck, but they did. So if someone simply disappears into the abyss, or disappears into fire... there has to be a small part of us that is willing to accept that they MIGHT be still alive.
Since Disney took over Star Wars, it has been written like a soap opera. Less concern with delivering a complete story, and more concern with keeping it going for as long as possible, and if loose ends get tied up great, if not, oh well. I don't care for that personally. With Disney's habit for cancelling projects on a whim if they under perform, I think it is even more crucial to NOT have as many loose ends as they do, you should be prepared to wrap up the story relatively quickly and tie off those loose ends as if Disney could bring about bad news tomorrow.
Gravity falls has mature content but a completely different type of mature content. I was not comparing them as apples to apples... I was making the observation that if you are willing to have one show at given time slot with clearly adult themes, then you can't make the argument that Star Wars: Rebels is a "kids" show and should be treated as such, when it follows a show containing equally (more imo) adult themes.
Also I think this last season's finale was awesome (yet uncharacteristic) of the series or the season as a whole. That being said it still had a lot of these noncommittal elements that I am describing.