I just completed an entire 50 count jar of arena runs in one sitting. The most I've ever done at once by about 40. I've never liked the arena, that kind of monotony mixed with random bouts of "haha 1-shot crit of death, enjoy your wasted rl dollars" never really attracted me. However, with the introduction of the smithy and the chance of improving my armor I jumped right in.
So now here I am, I've completed 76 team matches and another 40 or so solo matches. The vast majority of these were perfects. Through all of these runs I've not received an invite. I've read the posts saying "70% of people doing arena have them" and "these are rare but not too hard to get" and I sit there wondering "How is this not adding up? RNG is one thing but this..."
I would like to propose that the next time you design a system like this that you consider putting in some sort of ceiling. A slowly increasing chance of the drop the more you run the event. It doesn't have to ever reach 100%, but consider games like D3's legendary system. The more runs you make without a legendary actually increases the drop rate until you get one then it resets.
That way, even though you're giving us a reason to continue spending $100s of dollars on an event, we're not walking away so angry and bitter that we vow to never buy into another simucoin event again. At the end of the day you want to make money and we want you to make money... there has to be a middle ground here.