Thanks. Based on your calculations where you show 79 data points, 15 points with a Republican oversample, the likelihood of that kind of skewed result (or more skewed) based on approximation via normal distribution (Vassarstats.net) is:
< 0.000001 ie 1 in a million.
So either the pollsters are crooked or GOPers are more shy than Dems.
Bottom line, any poll winds up with an assumption...either created or by happenstance of response....on the weight of an election. IF Dem turnout is TEN percentage points more than GOP, THEN perhaps Hillary is way ahead. But that has no basis in reality. As the OP stated, Gallup has party Id EVEN. Now pollsters could use other methods, but it is reasonable to state they Party ID question is even.
In 2012, If I recall, The Dems only had a 3 point advantage in Party ID polling at this time of the year. So from that score, the GOP is already polling 3 points better than 2012.
It is true this election is going to be bit odder than any since the Perot elections, because some of the particulars are all over the map...like Trump getting big Latino and Black support in some polls, and not in others. Like Dems voting Trump and GOP voting Hillary.
Then you have the Sanders voters, and Johnson polling above what I personally think his name recognition is.
So this election could be a real watershed true shift election...meaning....none of the usual models are going to work, and if they do, it would probably be dumb luck.
I see this as globalism vs nationalism, and Hillary’s corruption vs Trump’s perceived personality issues. That has the potential to provide a very unusual set of voting patterns in Nov.
And we haven’t even made it to the debates yet...and Trump has yet to even start a traditional ad/local office campaign.
Throw in the leaks, and any pollster who is telling you they have this nailed is lying.