SSPs are often buyers on each other's exchanges and publishers often make ortb2.6 requests directly to ssps or dsps. Some DSPs, such as Microsoft, may act more like an SSP in certain contexts. The problem this sentence seems to be solving of 'don't relay this field' or 'make sure you edit this field for the recipient' should be expressed another way.
SSPs are often buyers on each other's exchanges and publishers often make ortb2.6 requests directly to ssps or dsps. Some DSPs, such as Microsoft, may act more like an SSP in certain contexts. The problem this sentence seems to be solving of 'don't relay this field' or 'make sure you edit this field for the recipient' should be expressed another way.
This sentence just often won't be true when the publisher is a component seller, which is already supported by prebid https://github.com/prebid/prebid.github.io/pull/4658/files
I wouldn't mind clarifying language that the field is only in the context of the recipient of the request and should not be relayed to other entities.