Except this isn't entirely accurate. While I did show prominent cases to make the point clearer, there are still plenty of times more common people were exiled and came back creating more harm. It's just that these stories, as well as success (I'm not denying that) are neither recorded as well nor is that information as widely distributed[0]. But there are also more well known cases where larger deportations/exiles/banishment occur and the acts create whole new societies! In most cases those societies are not very friendly with the ones who caused their banishment in the first place[1].

The distinction is that we're trying to be intelligent creatures with foresight. You're absolutely right that effectively there is no distinction when the crimes no longer occur. But what also matters is if these actions are prelude to greater turmoil down the line. If it is, you haven't solved the problem, you just kicked the can down the road. And we all know when that happens, the interest compounds.

This isn't to say to not use banishment at all, but to recognize that it isn't so cut and dry as you claimed. And there is specific concern because we have seen how US deportations over the last few decades has created and empowered many cartels in Latin America. It is worth considering alternative solutions, as we're already affected by this result.

[0] Although this is an exceptionally common plot in many stories. Ones told throughout the centuries...

[1] Some examples may be the Israelites in the bible (fact or fiction), you could argue the Vandals or the Goths and recognize many countries formed through people being pushed out of one place or another and being unable to find a place to settle take up arms. It is true for the Normans and the Comanches. It includes the Puritans who fled to America. It includes the Irish Diaspora. There are plenty of instances where groups of people were pressured out of a region and came back to fight and create more bloodshed.