Oh, it's very difficult to tell a party's strength just from their level. There are many other factors, such as equipment and augments. The last 4 fights in the Arena are pretty tough, might need to proceed in the main storyline if you can't beat em. No worries though, you have all the time in the world to worry about the arena!
I would like to note that this game is not a sequel. Could you change that on the first post, mods/Indy?

Thanks!