Dan,
For about the first 50 years of the 20th century, noone cared about the 18th hole in the context that it should function as the ultimate end to the "crescendo"
Match, not medal play was the format by which most golfers played the game.
In most cases, the match was over before reaching the 18th hole, so it would seem that its significance, in terms of difficulty, when compared to the other holes, was nothing of note.
That all began to change with the marriage of television, golf and Arnold Palmer.
Suddenly, the 18th hole took on a critical role.
The thought that a golfer, especially a PGA golfer could "limp" or "safety" it home on the final hole in order to win a tournament, lost favor. Instead, the thinking changed, whereby the 18th hole had to be a challenging hole to avoid the "limp/safe" end to a tournament. Now, the 18th hole, under medal play format, took on a far more significant role.
Thus the trend for difficult 18th holes was born.
As Bobby Jones stated, "There's golf, and there's tournament golf"
So, the answer to your question is:
Depends on whether you're talking about "golf" or "tournament golf"