Imho Sith are (way) stronger than Jedi in general... Jedi won because they had greater numbers, were the good guys and Sith tend to fight among themselfes just as much as against everyone else.
When it comes to a 1on1 only a few Jedi can match a Dark Lord of the Sith and in swgoh... we have a fair (in numbers) 5vs5.
Well.. but then there is Chaze killing a whole Sith team by themselfes so i guess balance in this game is not as important to CG than making money from new Rebels.