While you could go as extreme as canceling Prime completely, it’s not the only way to send a message.
Stop watching Prime Video.
They have as many metrics for what gets watched as they do what physical products get clicked on. Their Video division will see that their viewership has plunged. They will have to report reduced engagement to those who control the budgets. This will probably take a while, because they probably expected to ride out the initial subscriber backlash. Stick with it and show them that in the long-term, they’ll make more money by not being greedy.
As to how you get your Amazon exclusive videos in the meantime… well, purchasing the same content on Amazon only shows them that they can make money in a different way through putting their “free with subscription” content behind a pay wall. You’re not hurting them in that regard. So look for other ways to get the same content, in whatever way your conscience and technical ability permits.
Those really help the NERPS go down better. Yum!