I'm inclined to say that this applies to most of the losing Republican nominees in recent past: Mitt Romney, John McCain, Bob Dole.
I suppose this can in part be attributed to that odd habit of the American electorate to vote the less experienced and/or less qualified candidate into office (applies to 2016, 2008, and 2000 for instance), except when it's an incumbent president running for re-election.
The last winning, non-incumbent Republican nominee which I considered to be sufficiently qualified for the job was probably George H. W. Bush in 1988.
I think the tendency you mentioned has a lot to do with a combination of the Next-In-Line and Pendulum effects. Oftentimes the third term nominee of a party (or, for that matter, the challenger of an incumbent) is a runner up from the last open cycle that had since gained a lot of relevant experience that qualifies them even further than they were during their first run. They're qualified, but the country is almost always in the mood to reelect the incumbent or for the other party to control the White House after two terms.
In that regard, 1996 is a really underrated race with just how qualified both of the major party nominees were. Bob Dole was immensely prepared to step in, and Clinton obviously had already been on the job for four years. I think it's often overlooked because Dole ran a bad campaign and didn't come particularly close to winning all things considered, but this was probably the most "yeah we'll be fine no matter who wins" race in recent memory.
