This is an interesting question...or series of questions.
Routing today compared to the Golden Age (and prior...and through the 1960s) is much more complicated in my view. Regulations, liability, development, various client voices, environmental, cart-dependency and property values. The last, property values, outlays an extreme affect: That being that there is rarely such thing anymore as "white space" in designs. "White space" being the triangles or "un-useable" parcel areas which many years ago would have been forgotten and acceptable in routings. Today the necessity to fill every space is too often a first priority.
Remnant land is hardly ever a byproduct of today's golf courses. Of course, there are exceptions and these are often the best finished products.
Yes, it is very possible to design on flat or gentle land, a core course and create short walks between holes.
And yes, many of today's courses are built where golf "is not supposed to be played." And, yes, this causes walks (often) and carts (almost always.)
But — to carts — let's not take the position that they are purely bad for golf. Had motorized carts been available in the 1800s I am certain they would have been embraced by many golfers. It would disgust all among us, certainly. But so, too, would the motorized vehicle have been embraced in that age, and it would have been tempting to us all.
I, for one, applaud golf which can be walked. I look for it in my own work, but often fail at the experts who have taken every class in hand tying.
Have carts weakened routings? If you take the primary position that a golf course built where one "should not go" because of site or terrain constraints is "weak" in and of itself...then yes. But, if you adopt the notion that such courses have a place in modern golf, then you must look beyond the distances between sequential holes to whether the routing is ideal beyond the constraints of the site. Does it surprise? Thrill? Provide a sense of adventure and intrigue?