My opinion about what to do with factory seams that had lead in them has evolved over the years. Personally I believe that lead done correctly is better than any polyester based filler. I have no experience with the epoxy based filler but I still think lead being a metal and water proof will last far longer. (if done correctly) Problem folks have with lead is that they don't know how to correctly apply it and then use aluminum oxide sandpaper over the lead. So screw ups, defects, happen with the lead and paint applied over it, and the lead gets blamed.
Done correctly, lead will last a lifetime. And if you observe proper safety precautions it is no more dangerous than spraying iso based urethanes.
On lower end stuff I feel any polyester or fiberglass filler will suffice. Lower end stuff is probably a good place to use epoxy based fillers (on factory seams) especially if you have to apply it fairly thickly, like at the factory roof to 1/4 panel seam on a Fox body Mustang. When I was rebuilding early on we did a lot of those cars and used polyester based fillers and a fair amount of them would crack there due to the amount of filler required. Didn't really seem to matter whether we welded the entire seam or plug welded it.
Just my opinion.