They are not sending the whole candidate block, only block header is needed to mine nonce, to use timestamp as a nonce, to use block version as a nonce.
Sure, but still? Multiple times per second? Seems a long way off from the once a minute ranochigo is experiencing.
I suppose such a question becomes less relevant with Stratum v2, as individual miners will have the ability to select which transactions to include and create their own candidate blocks.