While this is true for the casual user who just uses RBF to bump the fee, it is not necessarily true if you know what you are doing.
Unfortunately that's not as easy as it sounds.
Especially since quite a lot of people believe they know what they are doing. Probably way more than actually know what they are doing.
You can change the value of both the change and the recipient outputs, so it is not clear which one is which.
I guess this won't be happening quite often since a transaction usually has a reason. You can't just pay someone less than agreed on.
Therefore in most cases it would need to be subtracted from the change, i assume.
You can instead include another input and use that to bump the fee, leaving all the outputs the same.
This would mix more outputs together which is generally worse. Especially for people who are not that good with coin control.
Further this will create one output which is guaranteed to be deemed as a change output by an observer.
You could instead replace the recipient's address with one of your own (unused) addresses, and make a second totally separate transaction to pay the recipient. The transaction may only have 1 output and no change.
This might work for generic amounts. But for specific amounts (e.g. 164.21$ in BTC at time X) that might be quite easy to reveal.
At least it is by far not as privacy-preserving as just sending a single transaction with that amount.
I think a better idea would be for Wasabi to allow RBF to be enabled with an option hidden in the settings somewhere and with a pop up warning it could decrease privacy, so users who know what they are doing can still use it, while those who don't appreciate the risks wouldn't.
I'd like the option, definitely yes.
But bumping the fee will most likely always result in decreased privacy.
And i believe a lot of people will think they know how to bump it without revealing which output is the recipient and which is the change, while in fact they don't.
Privacy isn't a straight forward topic. It's quite complicated.