He was silly, but he was smart. His silliness was used to his advantage because it often meant his opponents underestimated him.
Remember how the vampire removed his coat or something and ripped off 7 grenade pins attached to him? (and then you'll say... !!!!)
Jotaro has the same aptitude minus that very entertainment factor that made Joseph so awesome.
Current Joseph is also rather serious and not very uplifting. It was so nostalgic when he made fun of Polnareff for shits and giggles.