How to bring all replicas on a SQL availability group to an earlier state / point in time?
Yes, that is the correct approach. 

From my current understanding, restoring a back up on the primary alone would cause a data conflict (or corruption issues) on the secondary replicas 

Unless you remove the database from the Availability Group, you will not be able to restore the same database on the primary node.

On a side note:
If it is just dropping one table (depending on the size of the table compared to the database size) I might consider restoring the backup with a different name and recreate that table in the primary. There are many ways to do that which is not the scope of this question.