It's a riff writer versus a song writer. Steve Clark was a riff writing machine and others in the band excelled in song writing/arranging (along with Mutt etc). It's the equation that is no longer in play. Vivian is a good song writer and good riffer but few people have the riff writing ability of Clark. For that reason, it's a hard and even unfair comparison. Few people in the world get blessed with the ability to really write memorable riffs.