I think you're right that King could definitely have done 100 issues (or 105 or 7 or however many he decided). I also think that, despite my own belief that sales were not down as much as people claimed (because of the confusingly reported cardstock variants), and my belief that double shipping always loses more readers for long runs than single shipping, that it was a combination of two factors:
1) Sales were down from the "expected" 100,000 units sold for Batman (My belief is that they were still in the 80,000 range).
2) King himself was really tired of editorial interference. Starting, of course, with Ric being the biggest example - for which he took an enormous amount of flak, despite having no responsibility for DC deciding to keep what he never intended to be permanent - but you can go back before that, with War of Jokes and Riddles being moved from a separate 12 issue miniseries with Gerads to being in the main title, twice a month, with four fewer issues, and Janin, who he loves, but is a completely different artist than the one he originally conceived the idea for. Everything after Knightmares was clearly rewritten multiple times to deal with editorial demands, and there was The Price crossover that clearly did nothing to improve the reception of Knightmares.
Now, I think Tynion's Batman run is actually pretty fun. I dropped off in the middle of Their Dark Designs, but I jumped back on with #94, and enjoyed Joker War (largely because of issue #98, Jimenez's stunning artwork, and the status quo shifts in the Batfamily that Tynion is clearly pushing that I like a lot with the Batgirls). I'm hoping that since he's clearly on for the long term, Tynion will be able to have a freer approach, similar to his excellent Detective Comics run. Tynion's Tec actually is comparable to King's Batman in terms of dearness to my heart - but his Batman run is just "fun" for me. And I don't think there's anything wrong with that. I am disappointed in the "year apart," but I personally don't think it will be a breakup, as Tynion has gone out of his way to emphasize Bat/Cat's love for each other all throughout the run.
I am glad you're back, though, and I hope you stick around for Batman/Catwoman in December! I'm personally incredibly excited about it!
In our reread earlier this year, I did find City of Bane had one major thing that really twisted it in my heart - the clear destruction of King's plan with the death of Alfred. With the revelation that Didio literally called King AFTER the issue was released in stores to tell him that Alfred's death had to stay, it explains the complete lack of preparation and feeling of lopsidedness that the death creates. Didio personally literally destroyed King's story with that phone call, and I'm very upset about it. (The explanation, as King revealed in this interview: https://youtu.be/jqA5OhFCWNU?t=1107 - is that Damian was going to be under Scarecrow gas, and Alfred's death was his biggest fear.)
That being said, I think that King did a masterful job of trying to write a satisfying ending with that swerve in the MIDDLE of already having planned his ending. I would argue that he DOES stick the ending - not perhaps as well as we'd have liked - definitely not as well as I would have liked, based on my love for issue #32, Cold Days, Knightmares, and The Beach - but issue #85 does work, in the end.
And honestly, given how DC screwed over Morrison for his Batman Inc plans, Tynion in his Tec plans, and so many other writers in Nightwing, Batgirl, Batgirl, Batgirl (did I mention Batgirl?), the fact that we got what we did, and we're getting Bat/Cat in the format King does much better than an ongoing run, the 12 issue miniseries, is pretty exciting for me. Much as I adore this run of Batman, I think King is simply much better at a more limited space, where he's able to control the details and ideas and threads without having to control 100 issues all together.
I very much hope that your friend will like the ending at least as much as I did, and that he'll be able to read the Catwoman 80th Anniversary short story as an exciting tease for what's to come in December.
Well. I hope that this thread doesn't become consumed with negativity towards Tynion's run. I started this thread two years ago because I wanted a place of celebration and happiness about King's run, and I think we still have a lot to enjoy.