No offense, but you kept buying pigs in pokes; even if Jagex hasn't manipulated the odds on Treasure Hunter, you could still be SOL due to RNG alone. Jagex intentionally doesn't reveal the odds in numbers, because that gives valuable information to the player, which would result in decreased key sales: when players don't know the average money they need to spend to get a certain prize, they're more likely to try it, and if they don't get it, they're more likely to continue trying due to sunk cost fallacy ("I already spent money on this, so if I don't get what I want, I completely wasted my money").
Until loot boxes become properly regulated, if you want to even hope for Jagex to reveal the odds of winning the prizes on Treasure Hunter, stop buying keys. As long as there are enough many addicts buying keys, Jagex won't reveal the odds, since they have no incentive to do so.