So I played against a team who is level 39 and I was level 18, overall my team is better than his 116 to 110, and of course I lost the match not by a low score but by more than 2! Why I say it's a lie and it's not about stars is because he's level 39 he could set his win bonus higher than mine since his level is higher than mine I can't not match it and gives his team more advantage than mine. that's why I don't think it's base on stars than it's base on win bonus.
I reckon there should be a limit on the win bonus you can put up to, then it can be base on stars.