Would disagree.
Not the 'older design' wing, but plain and simply, a lack of thrust at higher altitudes, with the older straight-pipe engines, and the early fans as well.
If you operated these, you would positively know....first hand.
Been there, done that.
Now of course, much has been learned in the meantime, but I personally consider some of the original wings (B707 for example) were first rate. And yes, vortex generators were employed to steady the low speed laminar flow over the ailerons (both inboard and outboard) but all this considered, the original designers did a
very remarkable job, and certainly had the fatigue issue under control, to a large extent.
The fuselage skin crown was a whole 'nother matter altogether....
Been there, done that also...and sadly, a Boeing ain't a Douglas, and never has been.
Donald W. built
very fine aeroplanes.
Just ask UPS...they
still have a bunch.