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Most of parameters there could be changed by witnesses without any hardfork.
By now the majority of top-witnesses have voted for linear rewards and zero minutes early voting penalty.
The actual consensus state can be viewed on explorer https://explorer.golos.io
My understanding why people are still bying votes is some sort of addiction to be on the Trending.
And actually it isn't always 50/90, because vitnesses votes are "split" between something like 25/75, 50/50 and 25/90, consequently the parameters can change a few times a day depending of who from the reserve witnesses is taken into the calculation.

I see

Then I disagree strongly with linear rewards and no curation auction window and full priced downvotes

I somewhat disagree with a curation slider too

Putting these all together, I'm not at all surprised at their economic failure

I don't think this economic failure have anything to do with the curation model.
And actually the failure of falling from $0.30 to $0.05 as it's the case of Golos isn't so much different to falling from $6.00 to $0.3 as it's for Steem.

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