Your thoughts are not wrong, but this is 4th and 17 for the game. It is not about routes, it is about situation. As
@soflagator said you could blitz, force a quicker throw and try to make a tackle. But lets play it the way we played it. The routes are irrelevant. All that is relevant is the line to gain. Remember the max # of players eligible to receive a pass is 5. and the QB can run so that is 6 that can make the first down.. So lets jokingly play a LB 12 or so yards from the LOS to "spy" the QB. Not necessary but whatever. You rush 3. You have 4/5 guys planted at the sticks to cover that 50+ yard width. Rule #1 as soon as guy gets within breathing distance of you it becomes man to man. Simple. And you have 2/3 guys behind the line to gain to DOUBLE anyone who ventures as a receiver beyond the line to gain. Defending anything short of the line to gain was irrelevant and defending specific routes was not relevant. you are defending the sticks. We were in soft zone with zero urgency to break on the ball. Simple concept simple instructions. When guy gets within breathing distance you cover like white on rice.