Point taken.
My take was that we picked this guy up late season when no other team thought enough of him to give him an active roster spot. The Dolphins let him go from their practice squad (I mistakenly thought he was on it when we signed him). Then (according to Wikipedia) the Cards put him on their practice squad and he lasted 4 weeks before being released. Again, that might not mean anything, but the Cards are a fairly successful team with some astute coaches who seem to have an eye for talent. It is hard to dismiss their evaluation out of hand.
He could turn out to be a ball of fire - a talent that was completely mis-read by teams for the past 3 years that had a good long look at him. Or, he also could be a scrub who played well on fresh legs when 2 of the defenses that he faced were poor to begin with (Washington and Philadelphia) and had gone through a long season and were worn down. If Bush is 80% of the player he once was, then he is probably better than Gillislee. I think that, given how little the team has invested in the guy, he is expendable.