Your list proves nothing. Parties lose sometimes. They lose when they have weak candidates or strong opponents. They win when the economy is with them and lose when it's against them. Sometimes the right conditions produce the right candidate, sometimes not, but you can't expect the wrong conditions to produce a good candidate.
Landon, Willkie, Dewey, Ford, Dole and McCain were weak candidates. Anybody running against FDR was bound to lose. Nor is it likely a Republican could have prevailed in 1996 (running against incumbent Clinton and spoiler Perot in prosperous times) or in 2008 (with economic crisis and all the hostility to the Bush administration).
If there were a strong candidate who could have beaten Dole or McCain for the nomination, that candidate would have gotten the nomination. Maybe that candidate would have won the election, probably not. But there was no such candidate. It was a weak field that produced a weak nominee who was weak in the general election.
That suggests that "our brand" as well as "their brand" has some real problems. Saying that Non-existent Imaginary Fantasy Dream Candidate was really stronger than the people who actually got the nomination is wishful thinking. You run with who you have and if you don't have a candidate strong enough to beat the feeble candidates who get the nomination, then you're worse off than the (now largely imaginary?) "GOP-e".
The reason Goldwater lost is simple ~ he gave away the 30% of the black vote previous Republicans had received AND he gave away the Social Conservative vote ~ maybe not as big back then as now, but the idiot gave it away.
Nixon is almost a special case since he later on won two times, but in his first race he was the GOP-e (liberal lite) candidate against the more Conservative Democrat JFK.
Nixon never ran that way again.
Pappy Bush won when the Reagan Conservative base still thought of him as their kind of Conservative. When they found out he was a GOP-e backstabber they dumped him like yesterday's garbage.
Dole and McCain failed to come to grips with the demographic realities of today's Republican party and gave too much head to the GOP-e. In fact, McCain hired on all of Romney's backstabbers and that pretty much nullified any social Conservative leverage he'd gained with Sarah Palin on the ticket.
Here's how bad it is for your boy Romney. His life's experience, his political and social beliefs, and even his voting record, who he associates with, his likes and dislikes parallel those of Wendell Willkie. Roosevelt was a sick man and his campaign ran through Willkie like (p..p) through a goose!
A NOTE: I've noticed almost none of the Mittbots are unwilling to discuss Willkie.