Yes, this poll was too broad for this site. Had it been specified into categories, it would have told us more. "Pop schlock" shows will always wind up winning (losing?) a poll of this sort here because folks here are very unlikely to have any interest, much less praise, for such things.
Plus, everyone's consideration of what is "overrated" is highly subjective, as it calls forth the question as to whether or not the show is actually overrated, as well as the question "overrated by whom?"
In the case of Dallas, I think the show was always seen to be exactly what it was— a "prime time soap" (as it was dubbed at the time, and the first and most popular of a very successful array of the same, which rapidly followed— Dynasty, Falcon Crest, Knot's Landing, etc.). Nobody thought it was anything more than that. So I don't see it as "overrated," though it had absolutely no appeal to me, then or now or ever.