I watch every game, Frost played with top six wings here, and regressed the last two years.
He's actually improved defensively, but he's a soft player, and he's not a play driver, just doesn't have a high motor.
Briere has no prejudice against smaller players, but he was a smaller player who played when the game was far more physical (the "clutch and grab" era), so he knows what he wants in smaller players. He excelled in the playoffs, when the game really becomes physical, and is looking for smaller players like himself.
Look at the progress Brink has made, work hard, got stronger and faster and learned to play hard off the puck, now he's a plus forechecker who makes things happen, and he creates offense. Or TK, another smaller player who plays a physical game.
Frost and Farabee play soft, Frost b/c he lacks strength and has always had an inconsistent motor, Farabee b/c since the neck injury, he's been unable to add strength. They have some skill, but not enough to compensate for bringing little else to the table. I think Briere saw them as players who'd disappear in the playoffs when checking is tighter and refs tend to swallow their whistles - and he wants to go deep into the playoffs when the rebiuild is complete.
Compare to Michkov, who is highly skilled, but also highly competitive and plays with an edge, like TK, he gets into opposing players' faces and won't back down. That is what I think Briere is looking for in skilled forwards.