25% is correct from an expected return point of view.
Let's model this, shall we?
Assuming three is 1% chance of getting 5% and 0.5% chance of getting 10%:
In 200 rolls, this will yield two 5% and one 10% drop.
This would mean the equilibrium pot is at 5000: 200 roll + 200*20*0.25=1000, -(5%+5%+10%)*5000=20%*5000=1000.
This would mean 1000 coupon yield for 4000 ingots spent.
This is ignoring the free rolls, I'm not sure if those contribute to the pot, but they certainly take away from the pot. If it doesn't increase the pot, it would mean that the expected return is LESS than 25%
It is POSSIBLE, that the actual return before Monday ended up higher because they set up some kind of minimal pot line that causes a refill to say 5k even if no ingot is spent. But if that is the case, they are doing you a favor, you should not take that for granted. (And maybe the reason the whole bug occurred is because they noticed this refill is being triggered way too often and decided to reduce chance of winning to mitigate this)
In other news, if the chance of winning was 1.5% and was reduced to say 0.1% chance instead, you are getting OTHER stuff on the 1.4% that was reduced, which means with this compensation, you are getting MORE than what you SHOULD have.
For once, will you people stop complaining when they actually did something right? Being greedy is not going to help anyone, it's just going to make them feel "Fine, if you are going to complain even when we do compensate for the problem properly, we are not going to bother in the future, you are going to complain anyway"
I place half of the blame of their future post-bug inaction on everyone who complain about this compensation.