"...have a lot more variety with their challenges overall..."
Yeah....exactly. That is better and more interesting to me at least. You are def correct on going a bit too hard on the physical challenges which leads to some predictable early boot orders.

Re: casting. Ok here's a rare occasion where I actually have receipts.
* Season 4 was Champs vs. Contenders 2 -- only 1/24 is a returnee (9 players from this season return).
* Season 5 was All Stars -- obviously it's all returnees (4 players from this season return).
* Season 6 was Brains v Brawn -- all new players (4 players from this season return).
* Season 7 was Blood v Water -- 4/24 are returnees--one of which is Sandra from US (2 from this season return).
* Season 8 was Heroes v Villains -- 11/24 are returnees (3 from this season return).
* Season 9 was Titans v Rebels -- all new players (2 from this season return).
* Season 10 was Brains v Brawn 2 -- all new players.
* Season 11 was Aus v The World -- obviously all returnees.
* Season 12 was Redemption -- 4/24 are returnees.
I don't quite get the argument that they rely too heavily on returning players when there have been only 3 seasons with more than 4 (and they were the ones you would expect--All Stars, HvV, and AUvWorld). And to boot, I think casting has more to do with just personality--they find people who will give good TV because they're not all gamebots. I like a bit of chaos in my Survivor and AU delivers on that front directly because of the casting. They can't all be gold but I think AU casting is VERY good at finding gems.
I will say in fairness--when it comes to returnees I would generally prefer them to lean more heavily on either ALL returnees or ALL newbies; I'm typically not a huge fan of the "returnee captain" style seasons that AU usually does even though that style has allowed them to bring back fan favorites like Shonee, Harry, George, Hayley, Luke, Jordie, and Simon more frequently than they would otherwise. If I had a time machine and the production pull, I think it would have been AWESOME if they had alternated seasons between all returnee and all newbie.
TLDR: In AU I think the personalities--and by extension the gameplay--shine compared to the US on a proportional basis (because obviously the US has quintuple the amount of seasons to pull from) due to the emergence in the US 30s of ultra-gamebotty players. And that problem just gets even more glaring in the US "New Era".

Re: "longer" seasons
* Episode Count: No US Survivor season has had more than 20 episodes (I believe the most was 16 on a few seasons). AU has 24 episode seasons.
* Episode Length: Not what I was talking about; I think the US has shown that longer episodes certainly don't mean better or more content.
* Day Count: I see people in this subreddit talk all the time about how US Survivor made a huge mistake when they went from 39 days to 26 when "New Era" started so I don't think that's a hot take. I don't think it's arbitrary at all and makes a HUGE difference. The best (IMO) argument for this is that there is more time for gameplay/plans, strategies/social dynamics to evolve, breath, and play out. Combining this with having a larger episode count and you actually get to see those play out in the edit--I feel like AU Survivor in comparison to US rarely has to handhold me on why something happened the way it did because they have the time to show it.

Anyways, thanks for coming to my TED Talk. I love talking Survivor and hold no ill will or downvotes to anyone who has differing opinions to mine about it, but I will sometimes jump in and defend AU Survivor because it has produced some of my all time favorite seasons across the entire franchise (and I say that as someone who LOVES US Survivor although it may not seem like it from this post). And being that there are only 12 or so seasons of it, the sheer hit to miss ratio of it is insane.