Computers autonomous or not have weaknesses of their own. They can be tricked and fooled in ways a human can't. A human can point that 105 mm tank gun, pull trigger, boom, target dead, because he isn't fooled by ECM decoys. Also a 105mm shell, this:
View attachment 6532233
Is a far beefier payload than a quad copter can carry. It also comes in many flavors for any job. HEAT, APFSDS, HE, HESH, smoke, and many more. Direct fire will never be obsolete.
Also the Booker is immune to a 12 gauge shotgun. A quadcopter isn't. In fact the Booker has a 50 cal M2 machine gun up top for AA work if need be, so that's a direct counter to the drone issue, 50 BMG:
View attachment 6532238
Tends to vaporize small air targets and even kill big ones.