GT1 World is not endurance and thanks to God for that. I love the cars, but could not stand to watch 3 or 6 hours of racing. The new format is fun and entertaining, with iconic cars and lots of overtaking. About the ballast, as John Watson said, after all, these series are for fun and, as ioan pointed, there are some endurance racing with these cars So I am a huge fan of the current GT1 World series.
But I don't agree with ioan about F1.