Well, this is something haunting any game with microtransactions which allow you to get power / characters.
As bad as it might seem, it has a simple purpose... to make money... without money, game cannot run, servers shut ... but thats another story.

About the matchmaking... (lets put SWB aside as that one is usually dominated by few guys who lvl freeze which is also a reasonable strategy)
For the arenas and decisive bonds, the higher rank you reach the higher probability to meet similar rank is... since power doesnt mean much in there (only treasured tools matter), its only about characters you have.
Sure, there are ninjas which simply dominate arenas due to their massive damage and are only available for money (such as Indra). On the other hand we have tons of really strong ninjas which are available for free (with some savings) such as GNW Madara, Swimsuit Konan, AC Kakuzu, Rin who dominates in arenas... and we also have a pure f2p friendly Zetsu. Its all about spending cps wisely during Fuku deals.

For the Matsuri...
There is a matchmaking based on number of wins (as mentioned by Tachibana Saeko), which in my opinion is a fair one. If the matchmaking was based on lvl, it would only motivate players to lvl freeze (and therefore making low lvl SWB even more painful).
Making matchmaking a power-based is basically ruining the idea to power up... all you would need it to get ninjas.

There is no realistic way to separate F2P and P2W guys. if you put a match making rule to "never-recharged" and "recharged", then even a guy who recharged only to get Gaara would end up with real whales.
As much as this goes, its unfair but thats how these games work.

Now just for a second, try to look on other side of that Matsuri match up... Almost (because there are exceptions) noone likes to fight guys half of their power. Not only its not even challenging because you cant lose such fight, but its also boring (no offense to anyone, the weaker side of this match up finds it boring too). It doesnt matter what power levels we talk about in here... 100k vs 200k / 500k vs 1M / 1M vs 2M... its still the same.

Many of us will let a weaker guy get free win and retreat... there are however 2 things related to this...
1st: Since there is limited number of revives, and we want to get 5 wins aswell, we simply cannot run everytime we fight someone weaker.
2nd: Since there is limited number of revives, we are saving retreats for groupmates.

But here is a small tip, which might get you more wins eventually... get 1 "main" team and use rest to sacrifice.
Once you win, there is slightly higher chance to meet someone stronger. So after win, swap to a single ninja team, just to die...
Then put main team back as you should get better matchup for you, and keep revives for your main team in case you dont...

Its not really fair way either, since it both gives you advantage and also ruins the idea of the event, but if you cant help yourself otherwise... you know what they say.. "the end justifies the means".