Since in relativity everything is relative to a frame, doesn't that mean that in relativity theory (RT), all measurements are observer-dependent? Doesn't RT historically precede quantum theory (QT) in that respect? I am asking this because it seems to me that there is a general presumption "out there" which amounts to saying that QT was the first physics theory to do away with the "neutral observer" axiom -- or, equivalently, to do away with the notion that it is possible to design experiments in which the result is independent of the observer. However, RT postulates that measurements of a given phenomenon by two observers located in different frames would typically differ. Even more drastically, RT postulates (or is consistent) with the notion that while objects outside each other's event cone may be moving at speeds higher than lightspeed, each such object will measure any other object to have slowed down to a sublight velocity as they enter each other's cone. Given these postulates, why is QT's observational dependency postulate made to be the earliest historical acknowledgement of an observer's influence on the result of an experiment?