Regarding both questions, for now this is its performance... Maybe we change it at any time, but if you want to change it now you will need custom development. As we don't offer this service you will need custom development.
In any case, if you are looking for a quick way to add the suppliers to your products, you can use our premium add-on ATUM Export Pro. With this add-on you will be able to export almost any kind of data in your site, in your case, products, import it on a spreadsheet to modify it in bulk (in your case adding the suppliers to each product) and then import it again to your site.
I leave you here the documentation of the add-on where you will find useful info about how it works: https://forum.stockmanagementlabs.com/t/atum-export-pro-documentation
And the link to the demo site in case you want to try it for free: https://stockmanagementlabs.com/addons/atum-export-pro/