Arena opponent PI

Why are the PI's of arena opponents so much lower than mine? Oftentimes they're 10-15% below mine despite being the same level and rank, and the summoners are roughly the same level.
I understand that the opponents in quests have lower PI because they don't have masteries, but arena opponents have full use of them.
I know the champs will fight based on their rank/level, but because arena points are based (somewhat) on PI of champs involved, it seems like we're getting robbed of points. This only really matters if you're worried about milestone rewards (would need fewer fights).
I understand that the opponents in quests have lower PI because they don't have masteries, but arena opponents have full use of them.
I know the champs will fight based on their rank/level, but because arena points are based (somewhat) on PI of champs involved, it seems like we're getting robbed of points. This only really matters if you're worried about milestone rewards (would need fewer fights).
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Comments
-Clobberin
I also know that Kang and Thanos teams are their own beasts in terms of masteries, so I will purposefully exclude them from the issue.
I know when I play against some random player on match 20 through 150+, they will have an identically leveled team to mine (3x 4* rank 3 level 30), and without any boosts my PI will be 10% higher than his. EVERY TIME.