Speed of the projectile actually doesn’t matter much at all for FPV drones or ATGMs, they help in catching up to the target but both methods utilize HEAT warheads which are not kinetic weapons. Upon impact an inverted cup of copper inside the warhead is heated and propelled forward by the explosion, this metal jet punches through the armor making a relatively tiny hole and igniting/penetrating vital components or the crew, it can also cause spalling on the inside of the vehicle.
Kinetic weapons on the other hand, such as armor piercing fin stabilized discarding sabot rounds fired from main battle tanks, rely on a solid metal core being propelled at high velocities and do lose power over long distances.
What does weaken HEAT warheads is the distance the molten copper jet travels, spaced armor makes sure it detonates farther away from the armor and exposes the heated metal to open air thereby cooling it somewhat before making contact with the actual vehicle. As the other comment said, badly spaced armor can actually increase the effectiveness of HEAT warheads but I’m sure soldiers keep this in mind when doing these types of modifications to their vehicles.
As for the point defense guns, those aren’t a thing on vehicles. We have seen small generators plastered on Russian “turtle tanks” but those are to power electronic warfare units on the outside of the spaced armor, these devices block certain radio frequencies in a short radius around the tank in the hopes of breaking the connection between a hostile drone and its operator.
You have a point there yeah, I’ve seen drones get stuck in netting/windows of vehicles without detonating, something that could technically happen to an ATGM but way less likely. I was more thinking along the lines of solid metal cages where they might be redirected due to the angle but almost always detonate.