The GOP does have superdelegate equivalents. It's just a smaller proportion of the total delegates and some of them are bound to the state winner on the first ballot. 15% of DNC delegates are superdelegates, it's like 1% of RNC.
The Democrats are moving in that direction however, as this was part of the Convention compromise (the Sanders people wanted to eliminate them completely):
Under the reform package, in future Democratic Conventions, about two-thirds of superdelegates would be bound to the results of state primaries and caucuses. The remaining one-third – Members of Congress, Governors, and distinguished party leaders – would remain unpledged and free to support the candidate of their choice.
Superdelegates like the DNC's couldn't have stopped Trump, he got a first ballot superdupermajority, 70% of the delegates. By the time the primaries were over he was already at nearly 60%. He even got 45% of the popular vote.
The problem would have been the same problem that the GOP faced in 2012 as well as this year. There was no one main opposition candidate. There were three.
Trump won Super Tuesday (595 delegates) by popular vote over Cruz-Rubio-Kasich-Carson: 34%-29%-22%-6%-6%.
Trump won the next week (393 delegates) by popular vote over Cruz-Rubio-Kasich: 37%-31%-11%-17%
Trump won March 15th (366 delegates) by popular vote over Cruz-Rubio-Kasich: 41%-24%-12%-21%
At that point Rubio dropped out. There were only a few races over the next month for under 300 delegates but Trump won 44%-34%-17%. On April 26th there were 124 delegates, Trump won 57%-20%-21% but these were mostly WTA so he got 111 of the delegates. He won Indiana 53%-37%-8% for another 57 delegates to zip. At which point both Cruz and Kasich dropped out and Trump won 70+% of the vote in the remaining nine states.
In 2012, you had the same issue. Romney-Santorum-Gingrich-Paul.
First two months: 41%-24%-22%-11%
Super Tuesday: 38%-27%-23%-11%
March: 35%-35%-27%-3%
April: 53%-25%-9%-12% (Santorum dropped out on April 3rd, Gingrich on May 2nd)
Romney only had 935 of the needed 1144 at that point but nobody else went into the convention with more than 190 (Paul) and the highest possible total was 250 for Santorum but everyone but Paul released theirs.
Hillary
and Sanders advantage is that they were the only two candidates in the race. Hillary got 55% of the vote and 60% of the delegates, Bernie got 43% of the vote and 39% of the delegates. Not a huge disparity. (In 2008 it was 48% of the vote for Hillary and 46% of delegates, 47% of the vote for Obama and 53% of delegates.)
Had there been a third candidate who could obtain 15% of the vote and make it say, 45%-38%-15%, who stays in until the end of May, it would have been far far harder for Hillary to have won even with the superdelegates. That's more of the situation the GOP has faced.
This happened in 1984, the last time three candidates had 15+% of the popular vote. Mondale-Hart-Jackson split the vote 38%-36%-18% for 1606-1164-358 delegates awarded from the primaries. Mondale was 335 delegates short. The superdelegates plus released eventually put him over 2191-1200-465-26 (Others). Jackson tried to get the rules changed because the 15% rule in a lot of DNC primaries had meant he didn't get anywhere near 18% of the delegates. Mondale at the same time was trying to round up as many votes as possible so it didn't go to a second ballot and delegates be released from their pledges.
