You can try Method by Mell, on this page (scroll down a bit):
https://sims3.crinrict.com/en/2011/01/tutorial-how-to-get-rid-of-unwanted-custom-content.html
The point is to sort through your .dbc files—bundled custom content—one at a time, rather than all at once. Hopefully the launcher will be able to display all the items in each single .dbc file, so you can uninstall what you need to from that bundle. But even if the launcher still crashes when you're looking at a particular file, you can delete just that file and keep the rest. Reinstalling whatever was in that .dbc bundle is a lot easier than reinstalling everything.