Not really. I am currently playing with 2 accounts. One is 681k strong - matched against opps from 649k to 893k power. Other is 184k string - matched against 174k to 212k power.
Makes perfect sense.
No, it doesn't make any sense at all. The way player power is calculated makes it absolutely useless as filter for arena fights. Player power is mostly determined by the champion power of the champs in your account. If you unequip some champs that you don't use actually and that are in your vault, the player power will be reduced, leading to easier arena fights. What has unequipping champs in your vault to do with your strength in arena? Do drivers in the 24h of Le Mans get into a lower racing tier if they unequip tuning stuff from their privat car what is waiting in their garage at home during the race?