What's the difference between partitions and many tables?
The key difference between having many smaller tables and having one partitioned table is that the partitioned table can appear as a single table in SQL statements. You don't have to mess around with views and triggers (the latter are probably also less efficient), it is all handled in core.

However, you shouldn't have too many partitions, else query planning will become too slow, and you will suffer from all the other problems that probably made you abandon a design with tens of thousands of tables.

Maybe you can use partitioning to your advantage if you manage to split your table into fewer partitions.

Partitioning is a comparatively new feature in PostgreSQL, and v11 has many notable improvements in this area. So if you want partitioning, use v11 by all means.