Hi ,

The moment you dupilcate a product lots of dependent table are getting duplicated such as its stock in stock .move table,

Go to :- Warehouse - Traceability -Stock moves and search the product and delete the stock moves, if stock move is in confirmed state, It will generate a warning, Then you need to connect to your database postgres and then check in stock.move table with that product backend id or SKU and delete it from backend,

Then only you will be able to  remove that product.

A good way to create products in large quantities is to use csv files.

1 Create a product
2 Export his fields in a csv file
3 Use a spreadsheet to add more products quickly
4 Import the csv file with all the new products

This is to be performed on a test DB, and must proceed step by step and make checks.

I created hundreds of products using this method. You can also import images of products from a csv file.