What you’re asking for is kind of weird. Think about it.
Let’s say the game has a probability fairy and guarantees a 50% rate. The algorithm would be, “If I devoured last time, don’t devour this time.” Now imagine if that would make you feel better.
It means there are turns where you know, with 100% certainty, if you use the skill it will not devour. That means you’re going to have to waste a turn if you ever want it to devour again. You won’t like that. There’s going to be some match where you’d really like a chance to devour twice in a row, but tough cookies you can’t.
Worse, imagine how a 7% chance would work. It’s really exciting if Megavore procs, but imagine if the game is carefully regulating the probability such that if you’ve seen 7 procs, you’re going to have to make 63 matches before the next one. Does that sound fun?
That’s the deal with probability. You’re always hoping to hit the “good” end, where you’re running above 50%. It can happen and it makes for fun stories. It’s not so fun when you hit the equally likely “bad” end, where you run below 50%. If the probability is enforced, then you can never hit either end but overall it turns out things aren’t as fun that way.
A lot of people would rather see no random-based mechanics at all. Most strategy games try to eliminate completely random probabilities. (There are some that depend on it, yes, but the popular ones tend to let you control the odds. For example, in Risk, it’s your choice if you want to take a 50/50 battle or wait until you have enough troops to have an advantage.)