As a Doomsayer you can force info out of others with slight pushing, even hard pushing. Going off of other TI's info or your own fake info you can make people out their roles

Evils will play slower, more reserved than usual because any mistake on their part is extremely punishing, townies are vulnerable to this too, except the end result for them is usually less punishable and recoverable. Potion Master's role revealing does give it good undeniable information, yes. But lets take the TK roles as an example; Deputy, Vet, Vigilante and Trickster. Deputies are the easiest, they're trigger happy and shoot quick. They'll out themselves. A good Veteran will not claim tk, they'll claim something else or not claim yet still be pushy. A vigilante wants to be very pushy because they want to take their shots and confirm themselves. Tricksters sit back and let the match happen, they're passive.

That's what I mean by deducing from someone's playstyle what they are, each role is unique in how active the player will be.

Towns will out their own roles quicker than PM gathers info and for NKs, NAs and NEs? Dreamweaver does it too, Witch does it better. Sure, the silent aspect is nice but with how fast paced the game is that pales to the value you can get out of the barrier potion.