Masuri matches based on level first, which means unless you are lv 95, power doesn't enter into matching consideration.

+/-5 is well within what is "normal", it can get as far as +/-10 w/o adjustment from what I understand and even further when there is a win/loss adjustment, so it can be quite bad.

In your particular case, you have the misfortune of facing someone who is way more powerful than player usually are at a particular level, either a level freezer or a ptw. Both of which negatively impact the average players in not just masuri, but also sage.

As for arena, ranked is hell, I more or less gave up. All it gives are some rare frags anyway, most of which I don't really need much. I finished the 15 win event in around a hour, after around 25-30 total fights in training, along with 8 arena quests so i was using a number of weird teams doing it. Life is much easier in training.