This isn't some fringe feature they're deprecating; the official documentation uses these interfaces in its examples; they're literally telling you that's the correct way to use the library and then the next moment they're telling you it's not.
Every service has their own snowflake way of handling iterating over large amounts of keys / resources. I can see it as a massive pain for them to upkeep that within boto. Ideally they would have done the opposite and introduced these abstractions to the other SDKs, but that would be a little too customer obsessed.
Being slightly dramatic but if the plan is to use Smithy make all the SDK as dumb as the lowest common denominator across the SDKs, I might as well use curl and interact with the API directly now that curl supports Sigv4 https://curl.se/libcurl/c/CURLOPT_AWS_SIGV4.html
