I distinctly recall seeing the 1983-84 syndication ratings in that year's World Almanac. Wheel got about a 16.0 rating; Feud pulled an 8. Still respectable, but Feud was pulling double digit numbers and was the #1 show prior to that.
Not sure how Feud did in its final year, but I do recall reading that, during the same season, Lange's Name That Tune was canceled with about a 6 rating. Nowadays, that's a Top 5 show.
I do know Tic Tac Dough was in the Top 5 in the early-80s, but I don't remember how its ratings declined because of Wheel.