Not quite. The reason we have primaries (instead of smoke filled rooms) is because of the disastrous 1968 nominating contest, and the McGovern-Fraiser commission which began almost immediately after Nixon took office and continued work almost until the 1972 election (I'm not sure where in there exactly they got their recommendations in place, but it was before 1971, when McGovern resigned).

The reason the Democrats have so many super delegates is because of the Hunt Commission, however, which comes more than a decade later; formed in 1981, it publishes its report and recommendations in 1982. The nominating contests under the new rules were 1972, 1976, and 1980. McGovern won very cleverly in 1972, in large part because he knew the delegate rules better than anyone (he helped write them on the McGovern-Fraiser commission, after all). It took his opponents much longer to figure out how to campaign and where was worth campaigning. Carter, in 1976, was similar able to take advantage of the new primary rules and use early victories (before the other candidates were really paying attention) to become the front runner in a crowded field. 1980 is more complicated because Kennedy tries to "primary" Carter, who a sitting president. I'll mostly ignore 1980 because it's a strange case (1976 when Reagan tried to primary Ford and 1980 when Kennedy tried to primary Carter are the only real examples of this in the modern primary era--both failed).

But the other things to know was that in 1972, McGovern got creamed by Nixon. McGovern won only one state (Massachusetts) plus the district of Columbia. It's the most lopsided electoral college vote in history, if I'm not mistaken. In 1976, Carter won (he got 51% of the popular vote to Ford's 48%) but this was the first election after the Watergate scandal and (in addition to a struggle economy and the fall of Saigon) Ford had already pardoned Nixon. Any democrat should have been able to win that election. In 1980, when Carter went up against Reagan, he carried only six states plus DC (again, one of the most lopsided victories in post-War history, though 1984 was even more lopsided).

The Democratic Party, which had since the New Deal been a "big tent" coalition of Southerners, Liberals, union workers, urban machines, minorities, peaceniks, etc. etc., was worried that McGovern and Carter failed because they were "factional" candidates. McGovern, who people in the party said stood for "acid, abortion, and amnesty [of draft dodgers]". Actually, it was legalization of marijuana, abortion, and amnesty, but it sounds better with all "a"s so that's how it was remembered--this wasn't a far away criticism, but was originally coined (anonymously) by the man who was briefly McGovern's running mate. He was seen as a candidate that was popular with "the Youth" and the lefties and the anti-War crowd, but couldn't appeal to the other parts of the coalition. Similarly, Carter was seen as a Southern "factional" candidate (he was the first Evagnelical president) and his lack of broad support--particularly in winning over working class whites in the North who became "Reagan Democrats"--was supposedly because of his factional base.

Super delegates were supposed to put the thumb on the scale a little bit and prevent such "factional" candidates who would be "bad for the party" from winning. Whether this theory is right is debatable, but Mondale and Dukakis (after super delegates were introduced) didn't do much better. It's pretty easy to make an argument that they're an anachronism that have never actually mattered once in a Democratic Party's nominating process (the closest was in 2008, where, just to emphasize, they didn't matter).

There was also a bitter convention fight in 1980, between Carter's people and Kennedy's people over actual things on the platform, and the super delegates were also supposed to put their thumbs on the scale to prevent that (Kennedy tried to have the delegates vote to "unbind" themselves to Carter, among other things). But I got the sense that the factional candidate issue was pressing for them then the floor fight at the convention issue. They became a big deal the next cycle, for example, as they helped limit Jesse Jackson's prospects running as a highly faction candidates (mainly drawing on African Americans) in the 1984 primaries. Jackson heavily criticized the rules throughout the primary season, while Mondale (backed labor, which was still quite strong and had signed off the Hunt Commission rules) and I think Gary Hart (a young, handsome senator who was the candidate from the Liberal wing, who in many ways was trying to take over Kennedy's mantel and was a new favorite of the liberal wing until being pushed out politics by the first modern sex scandal in American politics in the 1988 primaries) were in favor of them.

Slightly more on them in this old answer from a month or two ago:

• Has there ever been a republican or democratic nomination that was decided by super delegates that went AGAINST the popular vote?

If you want any easily digestible way to learn more about presidential campaigns, I guess John Dickerson's "Slate's Whistlestop Podcast". They're addictive. I've listened to almost all of them at this point. I think if I remember correctly you're not American, but John Dickerson is a well-respected journalist who hosts Face the Nation, one of the major "Sunday Shows" where politicians traditional talk with journalists (the others on the big three are Meet the Press with Chuck Todd on NBC and This week with George Stephanopoulos on ABC, with Fox broadcast having Fox News Sunday with Chris Wallace [unlike Fox News the Cable channel, which leans heavily Republican, Wallace is personally a centrist Democrat] and State of the Union with Jake Tapper on CNN). Anyway, I don't always agree with Dickerson's take on current politics, but this historical podcast is excellent, well researched, and engaging. It's the only podcast I've encountered that entertaining and just one person reading a script (rather than ad-libs, interviews, or long scripted sections edited around pre-recorded interviews). It's a format that works much better than I would have imagined. I give the podcast my personal seal of approval. (You should know that my recommendation is basically a guarantee).

You're correct. The Democratic Party moved to a more plebiscitary system as a result of the 1968 Democratic National Convention, and all of the shenanigans that went on there, not just the riots. These changes were a result of the McGovern-Fraiser commission, which actually decreased the amount of control party elites had in selecting candidates. However, after Hubery Humphrey's, George McGovern's, and Carter's (for his second term, after beating out a challenge by Ted Kennedy for the nomination) failed candidacies the party felt they went too far in that direction, and as a result was selecting candidates that were unelectable in the general election . The Hunt commission was established after a bitter debate during the 1980 convention to fix this perceived issue, and resulted in the creation of super delegates.