First of all, a candidate's ability to get contributions is part of the picture. It's not something you can't dismiss. Nor can you assume that all candidates have equal drawing power when it comes to contributions. Some candidates are stronger than others in that respect. In any case, when Gingrich had big money from Sheldon Adelson, it didn't help him much.
Secondly, "level playing field" or not, I don't see Gingrich or Santorum or Bachmann or Perry or Cain doing any better than Romney against Obama. Romney won because the other candidates self-destructed earlier (remember Bachmann, Cain, Perry). That may happen to Romney as well, but the fact that it hasn't happened yet made him the stronger candidate. Money and endorsements might have given Romney a greater margin for error, but in a weak field, he did have more experience as a candidate.
When all this anti-RINO stuff started decades ago conservatives had a single qualified candidate they could rally around: Taft or Goldwater or Reagan. That hasn't been the case for decades. If there really were a strong, qualified conservative candidate in the race, the bellyaching would make sense. But then if there were such a candidate there wouldn't be any complaining, because he or she would have won. The problem isn't with outcomes so much as it is with inputs: the good contenders just aren't there.
Bellyaching to you is standing on principle to me. I'm not interested in participating in politics if I can't find a candidate who represents my views. Romney won because he brainwashed ignorant, uninformed or shallow voters with expensive, false advertising and he got endorsements and all kinds of biased, open and backroom support from party leaders. Everything Gingrich and Santorum said about him being a bad candidate for the general election has been proving true, e.g. he can't outspend Obama 20 to 1 like he did to them, therefore he can't get his poll numbers up. Adelson's money never came close to Romney's. Ability to raise money in a primary is irrelevant to the general election, where all the anti-Obama money only has one place to go. Case in point, Adelson is contributing to Romney now just as he and other donors would to any candidate. The only donors who wouldn't would be liberal ones who are for things like abortion and same-sex marriage, whose money I would passionately reject anyway. They're the last people I want my party to owe anything to.
We had a lot of good candidates in our primary. In fact that was the problem, we had too many, and they split the vote against each other in a lot of states. But the key factor was that the big money donors want a liberal GOP party, and not enough conservative groups participated in the primaries by backing a candidate early or donating money. It was a strategic mistake by the base of the Republican party. They could have defeated Romney if they had a better strategy and put more money on the table. Bottom line, the GOP establishment is at war with Christian conservatives, and The Battle of Romney in the primary is just as much a chapter in that war as is The Battle of Akin.