Why would someone who is willing to pay for supporter now no longer being interested in paying for it because of this? Your break even argument starts with a lot of assumptions that are merely speculation based on your assuming most people would behave exactly like you.
The idea that here are 4 times as many people willing to spend $10 for a second team than there are willing to pay $40 for a second team plus the current supporter features is largely untestable, but certainly not absurd. Given how many currently play the game for free, it's seems a reasonable choice to me.
And as someone who has been a supporter for over 4 years, I don't find there to be anything terrible about asking those supporters who want a second team to pay for it just like the non-supporters who want a second team. I actually appreciate it, as it means only those who are truly interested in a second team, whether they are supporters or not, are going to be members of Utopia. (I wish they'd come up with a better name, though.)
Your assumption that the support features and the second team have to be competing alternatives is simply false. They are two different products offer by BuzzerBeater. A person can buy one or the other, or both, or none.
The way the second team is being instituted, it really has nothing to do with trying to boost supporters. But it also doesn't do anything to lessen the value of the supporter package to those of us who consider supporter worth it's cost.