In Product list page magento uses product flat table for better performance ,

Because at list page we have very big number of product that is why people uses flat table instead of eav But in your case you have big number of product and indexing causing issue that is why you cannot updating the flat table.

So that's why you want to disable the flat catalog.

My suggestion is that if you do same then load small number of product at list page like load 15-20 product max to per page then only you get good page speed Otherwise ti take too long to load page and sometime you may face issue like server time out.

So if you disable product then reduce number of product per page at category listing.

In Product list page magento uses product flat table for better performance ,

Because at list page we have very big number of product that is why people uses flat table instead of eav But in your case you have big number of product and indexing causing issue that is why you cannot updating the flat table.

So that's why you want to disable the flat catalog.

My suggestion is that if you do same then load small number of product at list page like load 15-20 product max to per page then only you get good page speed Otherwise ti take too long to load page and sometime you may face issue like server time out.

So if you disable product then reduce number of product per page at category listing.

You can see different in performance by installing this extension in your local(developing) system

https://www.mgt-commerce.com/magento-developer-toolbar.html