Hmm you both have points.
Thinking about Unstable Gas, it's a rainbow card so it would be logical that it's somehow stronger than a mono imo, but yeah it seems so much stronger.
The reasoning behind the 15 damage cap was specifically aimed at arena abuse: i divided 100 by 6, got 16.66, so i made it 15 to avoid arena decks killing you by just spamming Tragedy from the start.
Now in realistic situations, arena decks have double draw, so it doesn't exactly fix the problem, and lowering the cap further would make the card pretty useless. In PvP, 15 damage isn't all that much (think Ruby dragon).
I could just put the cap to a number like 20 or 25, but i'm gonna think abit more on how to balance it more efficiently. My main concern here is that the text as it is now fills the card already, so i'd need simpler mechanisms (or vague wording, like Pandemonium's) aswell, because as technical as it sounds, it's a requirement nonetheless. That's why ndclub's idea, while good, could take too many words to explain for the current version of Tragedy.