Steve Gadd is famous because he revolutionized drumming. He introduced linear drum patterns. He had melodic ideas and great phrasing. He played for the songs, not for himself. TBH his soloing is rather stale these years, and whenever people go to his clinics they ask the same old questions (show me mozambique, show me late in the evening, 50 ways etc etc), which is rather passe. However without him there would be no Dave Weckl, amongst countless others that he has inspired. He was known for tremendous chops back in the day. Now he's sort of overtaken by your current favourites.
If u wanna see why he's great, seek out the records he plays on. He is the most successful sessionist by far.