While i agree with power first, i think that some adjustment for level should be made.
No, lv 50 with 60k power and lv 90 with 60k power are not equal, there is a LOT of talent choices that the lv 50 don't have access to.
And, a more extreme case, is lv 49 60k poewr vs lv 50 60k power, it might be only one level, but as lv 49 lacks summon, a lot of team simply don't work for them due to lacking a chase (I'm assuming that someone who is ptw enough to get 60k power at lv 50 would more or less have all the summons)
So I'd say 2k adjustment for lv 50 and 1k for 53 for the sake of summon and a 500 adjustment for every talent unlock would be reasonable. So a 60k lv 49, for example, would be matched against around 53-55k lv 90.
That said, it still doesn't accomplish all that much, there will still be players who always win and players who will always lose. For example, ptw with 6 tail naruto c*ually beat people 5-10k above them. So a 30k power lv 50 w/ 6 tail will still dominate his bracket. In fact, such player will dominate any except the highest power bracket.
On the other hand, players around 50-70k will probably never see the light of day as they will always be stuck on the highest power bracket, one where 80k+ rule supreme (adjust the power number down ward for later server clusters, but you got the idea)
IMO, the EASIEST way to give more people chances in sage and make it more difficult for a player to always win would be to have a "winner bracket" where all the top 3 winner of the last sage are placed(in case there is insufficent number of bracket so there aren't enough people for this, then all of the ones who won top 3 in last TWO sage. Keep in mind thou that there are 3 sets of top 3 per bracket, so 9 from each)
That way, only the absolute strongest who would always win no matter what would actually always win. All the others will at most win every other sage, which I think is fair (considering that winning sage is largely due to being placed advantageously as opposed to power/skill at this point)