> you'd have to nose down at a very aggressive angle to actually pick up speed

Sorry but what the hell are you talking about? Airliners are heavy, very aerodynamic, very easy to overspeed and they regularly actively brake on descent!

Unless there are other constraints on the approach, the point of the entire descent phase is to have the engines IDLING the whole time. The FMC actually calculates the descent profile backwards, starting from the earliest known constraint (e.g. a certain point at 5000 ft) and extending that back into the air accounting for the expected weight and drag of the plane. The descent phase often begins more than a hundred kilometers from the destination. Remember how they tell you in the cabin that the plane is starting to descent and you should put your laptop away etc? That's when the engines go to idle and if everything goes right, they won't spool up again until just dozens of second before touchdown. The goal of the entire industry is to have that happen as often as possible, on as many airports as possible.

If the plane is a bit heavier or less draggy than expected, or if the approach requires a steeper descent at some point, the airplane will calculate all that (in advance!) and let the pilot know (e.g. a DRAG REQUIRED message) and will require spoiler deployment. This is very common.