IMO, the masteries this season are too dependent on YOUR champion, rather than countering the enemy team comp/synergysing with your team comp.
Whats the point of adding a 6% arpen/mpen mastery. Why not just give all champions an mpen/arpen bonus?
I think it would be better for masteries to be more reactive. For example, 10% reduced crit damage or 4% reduced AoE magic damage.