Storing large documents - one table or partition by doc?

I’m storing thousands of independent documents each containing around 20k rows. The larger the document, the more likely it is to be active with inserts and updates (1000s/day). The most common read query is to get all the rows for a single document (100s/day). It will be supporting real-time collaboration but with strong-consistency for a simple schema so not well-suited to dedicated "document databases" that assume schema-less & eventual consistency. I won’t have great hardware/budget so need to squeeze the most out of the least.

My question is whether to put all documents into a single huge table or partition by document?

The documents are independent so its purely a performance question. Its too many tables for postgresql partitioning support but I don’t get any benefit from a master table and constraints. Handling partitioning in application logic is effectively zero cost.

I know that 1000s of tables is regarded as an anti-pattern but I can only see the performance and maintenance benefits of one table per independent document e.g. fast per-table vacuum, incremental schema updates, easy future sharding. A monster table will require additional key columns and indexes that don’t have any value beyond allowing the documents to sit in the same table.

The only downsides seem to be the system level per-table overhead but I only see that as a problem if I have a very long tail of tiny documents. I'd rather solve that problem if it occurs than manage an all-eggs-in-one-basket monster table.
Is there anything significant I am missing in my reasoning? Is it mostly a “relational purist” perspective that argues against multiple tables? Should I be looking at alternative tech for this problem?