How does a global inflation rate vote stop vote selling? It's a better alternative in your opinion, but I don't understand why a stake-owner wouldn't do both.
For practical solutions, have you looked at vote buying in Lisk? They had a cartel issue before EOS existed, and they're trying to change the rules, but I don't know the details.
You are absolutely right, a savvy greedy participant would seek out both.
The hope is that the average user gets an easy way to achieve their true goal, and by already achieving this, they do not expend extra effort to go further and join in corruption.
It's definitely not a great solution, perhaps arguably not even a solution at all, but it might be enough to at least help things and stave off corruption.
I haven't looked much into Lisk, but I have always been hearing about how it descended into a cartel. My reaction was always "of course." I'll have a look and see what they're doing!