First, it is not a weakness of Unity that your game was ripped and distributed. It has become an almost single button push task to rip an IPA from an iOS device, unless it changed in the past few months, in which case, it really is a single button push.
Second, it will only work on jail broken iOS devices. The number of jail broken devices in China is estimated at around 30%, the number of estimated devices in the US is estimated, informally, at less than 2%. Google will turn up these statistics for you, take them with a grain of salt.
Thirdly, the people playing a pirated copy of your game are most likely never going to purchase your game, you can tie yourself in knots over ripping off software or you can just shrug and move on. You cannot stop it, but you can do certain things to mitigate the impact, e.g. move certain key components on-line, add new content only available to those who make an in-game purchase, etc. Make a free “try before you buy” version that isn’t too limited so that people can check it out first.
I have a jail broken device, and it frequently has ripped software installed on it. I want to check out software and I don’t want to drop $10 or $20 or even $50 in the case of the some of the remote desktop apps only to find out it is complete crap. There is an expression: “Not worth the drive space, let alone the money.” I have purchased, at a quick estimate, around $400 of software for the various iOS devices in the house, and probably another $80 on Android apps. I am not condoning or encouraging piracy.
If you have never ripped a company’s digital product (software application, video, music, game, book, etc) then you might have a reason to get all huffy about someone copying your game, otherwise, don’t sweat it, it’s not a big deal. How much of your game was made with ripped software? Every single install of Windows is legitimate? Every software package you used is paid for or Open Source or free?
How much have you lost on a sale you never would have made?