ZeroX0666
Without retiring melinda have everything to be better that maria hill, i think you just changed the internal structure inside shield, on the future, if melinda does not die, she will have an agent level much higher that before, to the point that she might replace natasha in many missions, you know, natasha did many borderline impossible missions to earn shields trust, melinda does not need any of that, she is free to be promoted to much higher positions now.
there should be some YouTube videos out there, on the MCU, Comic, etc, timelines and alike, that is, if you haven't looked already. tbh, a fanfic doesn't have to be perfectly accurate; in the first place, fanfics are basically minor, non-canon, parallel timelines/universes branching off of the original "work", and expecting one branch to mirror another/ the original perfectly, would be insane, so don't stress too much. if you need help /advice /pointing in the "right" direction, just ask in the author notes or the chapter comment, and I'm sure someone will have an idea for you, they probably will whether you want it or not, lol