So look
Why can't the maths work? Say there are 5 features hidden under a pick, 4 of them pay maybe say a range of 10x-200x average. But the best one pays 200x-1000x average. There is a 20% chance of picking the best one, while 80% chance of picking the "worse" ones. Could that 20% not be implemented in the math?
So in your example, lets say the average of the "worst" ones is 50x, and the average of the best one is 500x right? If you make it an even pick then the average value is:
((50 * 4)+500) / 5 = 140x
If you were happy to accept 140x as the average win for the feature, then you could make the pick random.
However, that is a HUGE average win, so the feature would have to be pretty rare - if it accounted for 10% of the total RTP, then it would happen every 1400 games. Would you wait 1400 games for a feature which, 4 out of 5 times, averaged 50x? I'd be pretty disappointed...
So, what we would probably do is maybe have a 4% chance of getting the best one, and then a (96/4)% chance [24%] of getting one of the worse ones.
This gives you an average of 68x, which is much better in terms of balancing a game. BUT because the pick is now not truly random, we can't show the other outcomes. So you can now bring the feature in every 680 games if you want 10% RTP on the feature. That's a big difference.
It can of course "work" mathematically, but it is only an option if the outcome is worth it from a game design / player experience / maths point of view. And everyone has a different opinion of what is "right" and "wrong" in terms of game design and maths - and i don't just mean people on here.. i'm talking players, producers, maths guys, etc...