Well directed kinetic energy can be devastating and has been used for such effect since ages, for example the old canons with passive cannon balls. Rail guns are their new sought after variants.
The famous bunker-busting smart-bombs circa first gulf-war were fin stabilized old tank barrels packed with explosives. It is their weight, owing to the high density metals used in the barrels and their small cross section (and hence extremely high terminal velocity) that gave them their extreme penetrative punch. Enough to pierce through tens of layers of strengthened concrete, each several feet thick and explode with devastating effects underneath. It was very important that they did not topple in flight though. So stabilization was critical.
Even the modern anti-tank weapons are essentially glorified darts, but much, much heavier. They kill tanks by sheer kinetic energy alone. They have been found to be harder to defend against, compared to other variants like HEAT that penetrate tank armor by the use of a high speed, dense jet of liquid metal, or HESH which are sort of like cow-pies made of high explosives that set off spalling bending moments inside the tank 'hull'.
the main benefit of the small cross section is not increased terminal velocity through the air but rather to maintain velocity through the bunker (or armor in the case of the "sabot" or APFSDS anti-tank round you mention)
The famous bunker-busting smart-bombs circa first gulf-war were fin stabilized old tank barrels packed with explosives. It is their weight, owing to the high density metals used in the barrels and their small cross section (and hence extremely high terminal velocity) that gave them their extreme penetrative punch. Enough to pierce through tens of layers of strengthened concrete, each several feet thick and explode with devastating effects underneath. It was very important that they did not topple in flight though. So stabilization was critical.
Even the modern anti-tank weapons are essentially glorified darts, but much, much heavier. They kill tanks by sheer kinetic energy alone. They have been found to be harder to defend against, compared to other variants like HEAT that penetrate tank armor by the use of a high speed, dense jet of liquid metal, or HESH which are sort of like cow-pies made of high explosives that set off spalling bending moments inside the tank 'hull'.