It will invoice intense labor to try to remove all that grout and then regrout. Better to remove the tile as you said and start over

You don't grout over grout. At this point it's more than likely a complete do over. Depending on the type of pan you may need to redo that as well, which if tied into the walls properly will lead you down that rabbit hole as well. But that grout will not stay or last long at all, due to it being to independent layers.

You can see the sheet lines even in the close up. Plus the non removable sculpture attempt. 🤦🏾‍♀️ Complete rebuild. A proper rebuild. With proper slope and waterproofing. And please don’t choose porous marble. It’s a big enough problem when tackled by a Pro. It’s a nasty stained mess in the best of cases.

Buy yourself an industry bible. And read it. https://www.tcnatile.com/products-and-services/publications/218-english-publications/188-handbook.html

I don't think you'll ever be happy until you have this removed and hire a GOOD Tile Mechanic to install it properly . IMHO, anything else is a "Band-Aid" fix....