Regarding the bolded, it is all relative. Every major leaguer is an "athlete" even the fat ones.
What he's saying is less athletic guys have been able to get away with playing in the middle infield of late with the increased shifting. Odor is a good example imo. Without the shift, Odor is not a 2nd basemen. With the shift, because of his arm strength, he can play there and even be an asset.
Middle infielders, particularly 2b, are going to have to start to prioritize range over arm strength with the new rules.