The problem is that you're targetting the 'average DI team, which is not necessarily a good measure. If you saw the problem as coming from excessive arena income, you should have indeed targetted large arenas only through something like arena upkeep.
Yes, this problem might be offset by the improved attendance formula, but a young DI team who actually needs to expand his arena to feel these benefits will struggle mightily for no good reason.
"I don't know half of you half as well as I should like; and I like less than half of you half as well as you deserve."