Something like this might work, but I think the actual effects you've suggested would need changing. The chance of getting the silence card when you actually needed to silence something would be so slim, and most bosses are immune to Heavy/Slow. So I don't think those would ever be used in this "new" way which would defeat the purpose of changing them.

But in general, I like the idea of the cards doing different things on different targets.
But I also just think AST needs a buff overall anyway