Not sure I'd call them "busts", as both are aging WRs rotated out of the starting lineup (Cantu benched, McCullough returning kicks at WR4) in favor of younger, faster, more agile and sure-handed players.
I would think a bust would be more along the lines of a guy who rushed for 250/4.5/1125/15 last season and 250/2.1/525/5 this season. Or, say, the London Monarchs

JH