A proxy would also open up opportunities like serving cached responses for more static calls, which would raise your margin.
Careful, that’s supposed to stay a secret!
In a way it’s similar to a gateway in that you are composing different backend targets. Although it might just be a marketing neologism describing middleware.
Like if you aren't already doing "transform", you probably aren't reversing it.
Reverse ETL is marketing to differentiate to the customer that you're pushing data into services as well, so that it's read/write to all.
Of course the concept is amusing to someone talking about ETL, but the market moved at some point to refer to the first functionality as ETL and so this is just a change to differentiate.
Typically, reverse ETL starts with "all of my data is already in an EDW" and goes to "I want to push it to my various app systems."
Canonical example: pushing system of record information to Salesforce to speed and enrich the sales cycle.
Like "extract" isn't any more specific than a source and "load" isn't anything more specific than a destination.