Security News > 2020 > October > Friday Squid Blogging: Interview with a Squid Researcher
So not only have you eliminated by far the majority of messages, you've also broken the "OTP proof" of "All messages are equiprobable".
Using compression does alow you to change the encrypted message length, which for years was also desirable because reducing the size of a message had other benifits, not the least of which was cost, which is why the later Victorians were apparently "Code book crazy".
So with a true stream cipher that does not cause diffusion, the preprocess of compression if propperly done does cause diffusion in the message.
The way most OTP's in pencil and paper form are used they are actually block ciphers where the block is the size of the message underlying alphabet, unless the alphabet size is changed.
The point being you have seperated the changing of the message length and message statistics flattening, thus can optomise them seperately, as well as change them easily when required.