My understanding is that Let's Make A Deal and Hollywood Squares were in neck-and-neck competition for ratings in the early and mid-1970s, but I've never seen the ratings data to prove it.
I've seen that as well. I used to check out the World Almanacs; each issue has a list of the previous season's top syndicated shows.
Sorry to bump this, but I've checked the World Almanacs, and think the data within may be of interest.
From what I can tell, the earliest World Almanac to have syndication ratings was the 1978 Almanac, including ratings from 1976.
Syndication ratings, from the 1978, 1979, and 1980 Almanacs (game shows in bold):
October-December 1976 (pgs.422-423):
Lawrence Welk- 16.2%
Hollywood Squares- 15.0%Hee Haw- 14.9%
Name That Tune- 14.2%
Match Game PM- 14.1%
Price Is Right- 13.9%
Candid Camera- 13.8%
Wild Kingdom- 13.7%
$25,000 Pyramid- 13.4%Muppets- 13.2%
Truth Or Consequences-12.7%
Gong Show- 12.5%Jacques Costeau- 11.8%
$128,000 Question- 11.5%October-December 1977 (p.426):
Lawrence Welk- 14.8%
Hee Haw- 14.5%
Muppets- 14.0%
Name That Tune- 13.9%Price Is Right- 13.8%Match Game PM- 13.7%
Hollywood Squares- 13.5%
Gong Show- 12.7%
Family Feud PM- 12.7%
$25,000 Pyramid- 12.4%Wild Wild World- 12.2%
Candid Camera- 12.1%
Wild Kingdom- 11.7%
All-Star Anything Goes- 11.2%
Bowling For Dollars- 10.8%
Let's Go To The Races- 10.8%
November 1978 (p.429):
Muppets- 14.7%
Family Feud PM- 14.2%PM Magazine- 13.9%
Name That Tune- 13.4%
Price Is Right- 13.3%
Newlywed Game- 13.2%
Hollywood Squares- 13.1%Hee Haw- 13.0%
Lawrence Welk- 12.4%
Match Game PM- 12.0%...Havoc Struck- 12.0%
Wild Wild World- 11.6%
Vince Dooley- 11.6%
$1.98 Beauty- 10.7%Candid Camera- 10.5%
(These ratings are for total adult households. I have copied every listing that had an adult household rating, but not the entries that had entries for women, men, teens, or children only, Titles are based on those in the World Almanac, and may not conform to actual titles).