For the MRO?
No, actually you would gain significant improvement.
The parallax issue is more specifically from "odd" position shots where you cant get being the reticle on center. Like laying on the ground. The MRO suffers when the dot is at the extremes of the glass, from POI. Within the middle majority of the glass the red dot is still on POI like every other red dot.
Using a magnifier will place you more appropriately on center since it WILL have parallax limitations to even see through it. The dots always increase in size with magnification, a 2moa dot at 3x is 6moa. A 1moa dot at 3x is, 3moa. moa doesn't change at distance. 1moa is roughly 1inch every 100 yards.. its an angle thing. so a 6moa dot would cover a 12" plate/target at 200 yards.
If you maintain proper cheek weld and treat it like any other optic with parallax its irrelevant. I find the benefit with the MRO is the field of view. I would take the MRO with worse parallax than an aimpoint pro that gives me tube vision.
May not have been the best way to approach hand loading, but I shopped for bullets purely on the BC spec, always looking for the highest BC for weight. I'm not a hunter so terminal was not part of the equation, but the BC on those Sierra 77gr TMK (which I think is a hunting round) is pretty good It's .403 G1 If I recall correctly.