> The US Navy has lasers on their ships that could pretty effortlessly shoot down slow fragile drones

Transposing to the current situation, the Belarus/Russians will surely figure out defenses an apply these, but they tie up personnel, generating a cost and a loss of effectiveness on the equipment defended.

This kind of military harassment strategy was used by the WW2 French resistance, and certainly dates deep back into history.

It also creates media noise, attracting attention where the adversary wants to remain discreet. And successfully so in this Russian "AWACS" case