(1) is by the way False.
It is precisely by establishing epistemic standards for deciding when we are mistaken, and when not, that we are able to evaluate historical sources and even formulate the claim that they are "subject to power relations".
So your defence is rests precisely on the sort of underhanded equivocation being described.
Only Foucault already knew that, and had studied extensively how those "epistemic standards" have been established and developed.
That's part of the problem, those standards are not some objective yardstick, but involved in the same issues themselves (again: not for hard facts nobody really cares to challenge, like "water boils at 100oC" but for facts that people do care about, have interests invested in, and so on, whether they are political, pedagogical, historical, and so on).
>So your defence is rests precisely on the sort of underhanded equivocation being described.
Well, then again, your comment rests precicely on "vaguely know about the works described, so will attribute strawmans to them, as if those authors haven't already considered the naive solutions I'm proposing to the issues they study"...
Re (1) there "being a practical distinction" is irrelevant, if the distinction is of no practical use. At best one can self-congratulate himself of knowing the "real truth", while outside, the accepted truth is something different. And nobody in their right mind would just trust that person, or trust that "they" have the correct epistemology/methodology, when most disagree.
For example, in the 19th century South the "truth" was that "blacks are inferior", and that didn't change with a different epistemology -not to mention most scientists agreed at the time to the same "truth" in every "civilized" country-, only with different power relations and social work. In the end, it took a whole civil war. Any "methodology" will be applied (and accepted) once the power relations change (or are forced to change) not before. It's the power relations enabling the change of the "truth".
Heck, even in hard sciences, like physics, as Kuhn wrote: "a new scientific truth does not triumph by convincing its opponents and making them see the light, but rather because its opponents eventually die, and a new generation grows up that is familiar with it."
Which he fails to demonstrate - besides them using the same term for both (which everybody does).
He also fails to realize that "truth as some property of the universe" in many cases is only available through "truth as it matters to us" anyway. In which case, it's wrong to extend your claims to that too.
This is not just the case for things like morals, social norms, politics, etc., but also seemingly "hard fact" things.
For example, X historical event might or might have not have happened. Or might have happened in X or Y way. How exactly it did happen is "truth as some property of the universe".
Lacking a time machine though, and going through history (the academic endeavor), we only have access to it as "truth as it matters to us" - even sources of the time are subject to distortion due to power relations etc, and how we accept or not some source as valid and accurate is also subject to modern power relations, ideologies, and so on.
This "truth as some property of the universe" historical happenstance is thus not that objective in the end, in the sense that it's not (and will never be, without a Delorean) availabe in any objective form in which we can obtain it and use it.