I think a lot of people tend to keep low standards for IS (which is fair), but frankly I don’t think there’s any chance that the 2nd place prf skills was a one off thing just for Marth. With that argument, why did Eirika get one? If it was 100% Marth favouritism and absolutely nothing else, Eirika wouldn’t have got one, and future years wouldn’t get one.
I sincerely doubt IS would just dump the 2nd place prf skills after one year of it. As for the previous years that didn’t get a prf skill, who cares? Sometimes changes have to be made. You can’t go back in time, and retroactively giving them prf skills is not unreasonable, but unlikely.
And on the Marth favoritism: I don’t think it’s the sole reason IS gave them prf skills; CYL is probably the highest selling banner every year, and giving all of them something extra special (a prf skill) would just increase sales. Sure everyone grumbles about how 1st place isn’t special, but no one would ever not pull for a 1st place unit just because a 2nd place got a prf skill. However, people would absolutely pull for a 2nd place because they have a prf skill. Did IS Marth favouritism play some part? Perhaps. Is it the sole reason, and once he’s out of the picture, they stop caring? I very much doubt it.