I don't really think it's fair to say that they are deliberately switching things to work in their favor...That's why I asked to specify beforehand so there's no confusion. Remember, pokemon will have less energy as well as health to work with on that scale, so it helps to take extra care!
On that note, i'd like to tell you that you'll always have a say in the matter with these things. Don't like the arena? Want a different Equilevel/Equiall? Want to include a special rule? You can always come to an agreement before the match even starts! The 4/6 scale is often used for shorter matchups. If you wanted the standard scale, you have every right to let me or your opponent know. I'm sure they'd be fine with it!
And even if they didn't, know that no one can force you to to stay in a match you don't wish to participate in. So if you have a problem, please speak up! But I do recommend you stick with it to the end, even if things don't look good...Who knows how things could turn out?