You spent $400 because your win rate went down 0.2%!?

This is the calculation I've been making every time I think about buying a legendary summoner. How much would it need to improve my win rate for it to be worth it? Because it's a terrible value proposition in terms of CP, so it's only worth it if my win rate goes up considerably.

I don't know how many DEC you get per win, but let's assume 100. And let's assume DEC=$0.01. And that a Mimosa will give you a whole 1% (5x your recent decrease) increase in win rate from 55.3% to 56.3%. And that you win 20 battles a day. That's 40,000 wins before Mimosa wins you the extra 400 you need to pay her off.