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
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.
