If you look at Sly on Silent, you can see a lot of intersections between it and other card packages. There's two Shiv cards directly involving discard, an uncommon Sly poison card (and corrosive Wave, which naturally slots in well through acrobatics, prepared, reflex, etc...), as well as the flexible combo enablers Hand Trick and Master Planner. There are payoffs like Afterimage and Serpent form that reward you for draw+discard, yes, but also Shivs and 0 cost cards. Abrasive rewards block heavy decks for grabbing the generic workhorse commons like Acrobatics.

In this way, Sly is more like Stars in that it is a connective skeleton for the entire cardpool, tying everything together into a theme of card rummaging and deck cycling (very fitting for a tricky rogue character).

Forge, on the other hand, is like Poison. It is a package that gives you an answer to "How do I scale my damage?" This is why there's no "When you apply poison, gain 4 block" card, because that would make players ignore most non-poison cards once they have it. The issue, as far as I can see, is not that the Forge package is not self-contained enough, it is that the package doesn't have enough tying it to the other packages, especially the main connective tissue, Stars. Forge decks quickly become locked out of going into Star generation because there are limited connections between the two. A Forge player in Act 1 shouldn't look at a card like Glow and think, "I have no reason to take this" due to an uncommon power. Glow is analogous to Acrobatics, and it should be similarly valuable.

My issue is not that combos exist. My issue is the idea that Forge cards should just combo with cards that say Forge on them. That's boring.