There was a lot of boring football in the pre salary-cap days. Unless you were watching a team that could afford to stack their rosters with big-name players, the games could get awfully boring. I remember snoozing through a lot of 17-13 Tampa Bay/New England games (when Tampa Bay and NE were awful) during the 1970s. It was like watching two teams both trying equally as hard not to win.
Tampa Bay didn't join the NFL until 1976, and the Patriots had a winning record every year from 1976 through 1980 (they fell to 2-14 in 1981). And since Tampa Bay never played in the same division as New England (the Bucs played their first year in the AFC West, then moved to the NFC Central), I'd guess they probably didn't play each other very frequently.
Interesting tidbit . . . I did a little research on this, and it turns out that 1989 was the first year in which both the Patriots and Bucs had losing records!
At any rate, I have no doubt that there were some really bad teams back then, but if you go through each of the last 30 or so seasons since the NFL went to a 16-game schedule you'll find that there is no pattern at all to the frequency of downright abysmal teams.
Another interesting tidbit . . . The single worst game in the memories of a lot of NFL fans was the Monday night game in 1983 when the 8-7-1 Cardinals and the 3-12-1 Giants played to a 20-20 tie, in a game filled with dropped passes, missed tackles, and missed field goals (I believe both teams missed at least two field goals at the end of regulation or in overtime). I remember a sportswriter back then describing it as the most hideous game he'd ever seen -- and one which probably set the NFL back 20 years because it was on national television. LOL.