I may be wrong but I think you have to try to understand why we have reached a low point. If people were enjoying the stream, they wouldn't leave so why aren't they happy ?
Yes, there are natural reasons (this is basically just grinding right now) but I can assure you my book is full of great disappointment for this run and not only because of the Rom Hack. Some people don't like how we got rid of our teams for Optimization/killing a Mime, some people don't like how we stalled timers to obtain Democracy for a switch while the run was full anarchy until then ("reduced" anarchy but still anarchy). And some people aren't happy with Chat Leading (partly because it's linked with Optimization). They may be wrong but you can't summarize the lack of viewers/players by "the casuals just left"...
The returners belong to the community and I'm not sure seeing them leave is a good thing (you can see that with the activity of the subreddit for example). TPP needs players to be "alive" even if it makes us go in circles instead of progressing. More players usually means more Chaos (and not "forced Chaos" if you want to talk about Black) and the journey feels completely different with only "the core". Is it really about beating the game no matter how many people stick ? I prefer failing next to 10,000 people rather than obtaining a flawless victory next to 1,000 people...
I don't believe the majority of returners pushed for PC (or we would have been in a deadlock with a Kakuna on Day 1) and I don't believe the players from last year were "hardcore progressionists" either. They just played the game (trying to win of course but also enjoying it and caring about our mons). However, if you're talking about the majority which didn't even try the Strength challenge and switched Zapdos in Democracy, you know that it kind of ruined a part of the fun for me (and I'm not alone) and that I don't prefer them to "PC guys".
Back to the returners, I'm not sure they were the ones who called for releases (Charizard could have been deposited at some point to grind the others, the only other OP mon I see is Leech King and it's another debate) and triggered the Mime fiasco (they were gone according to you). You can probably try to blame some of them for trying to deposit/release our Flareon but was it successful ? No, we only deposited Flareon when you decided to lauch your Mega Plan.
The "B+Left plan" makes sense in theory but it felt awkward when you tried it : yes, B were needed to ensure a safe PC trip but "Spam B+Left" combined with the inputs of the people who didn't want PC just made the PC usage impossible (we even left the Center). It was a good plan but I don't think it's a coincidence if we deposited Ponyta when you left. Anyway that was not the point :p
I had a lot of fun during this run but now it feels like a parody of my own TPP experience : great moments then great disappointment because of our actions. As I said, I don't care anymore and that's particularly disturbing since I used to care a lot. It felt like Red, now it feels like Firered : I hope "the core" likes it.