In the late 90's, you had 3-4 choices as a baseball fan as far as routinely watching a specific team.
You watched your local team(s).
You watched the Cubs on WGN.
You watched the Braves on TBS.
There are many thousands of people who are Cubs fans right now solely because of the 98 home run chase. I was already a Cubs fan but I was 13 that year and Sosa going after 60, plus the Cubs making a playoff push, certainly solidified that. I would watch the Cubs in the summer when school was out. And when school was in, I would come home and tune into the last couple innings on WGN to find out if Sammy homered or not.
So yeah, in terms of growing a fanbase, it's unlikely any other Cub had as much of an affect on that as Sammy.