A wall still works in the form of an obstacle. Drones can not cover every inch of the border.
Do walls stop drug trafficking? Not really - there are tunnels, boats, planes, bribery and so forth.
Do walls STOP people. Not really, they make it harder for people to cross but that's it. Even if we had the kind of border wall East Germany put up with extensive physical barriers and shoot-to-kill border guards, people still ran for freedom and many made it.
If we really wanted to stop illegal immigration, we'd do it by really going after the employers and fining them so much that it really hurts as well as arresting, trying and jailing those involved.
So I conclude that the wall is marginally useful in slowing down those who want to cross the border without really addressing the issue.