I don't have any experience with Clipper Craft. However, Richard Press is always going to be comparing anything with J. Press, which we can all agree made excellent quality, hand-tailored clothes. He's a salesman at heart - it's hard not hear the "At J. Press, however..." after his quote in that article. I wonder what Press would say about old Brooks Brothers "346" jackets and suits - they were Brooks's lower-rung garments, but they often wear more hardily after all these years than the fancier Golden Fleece/Makers stuff. I also think of Corbin or Palm Beach, which were probably closer to Clipper Craft in terms of quality than 346 and are both great options when the details are right.

Any vintage garment is compromised to some degree by age. If it looks like it's in wearable condition, without flaws which will unduly hasten its demise, and if it has all the details and styling you desire, I say go for it. It's lasted this long already, right?

Well, to my mind, there are a few factors that differentiate the majority of clothes today from even a company such as Corbin, Palm Beach, and I assume Clipper Craft:

1. Union-made in USA. These companies may have been mass-producing "Ivy" clothes, but they were doing it in American factories, to a higher standard than is found for mass-produced clothes today.
2. Clothing culture. While not every piece of clothing was "made to last" the way a J. Press coat was by any means, especially department store fashions that had their eye on the next big thing, fast fashion in the H&M sense wasn't a thing yet, so even mass-produced clothes were made to last longer, hence our being able to buy them on eBay today.
3. Taste/look. As you have said yourself, there's little functional difference between a Clipper Craft Ivy jacket and a J. Press one in appearance. Contrast this with, say, a J. Press jacket versus a Uniqlo jacket - the Uniqlo may be similar in some ways, but they aren't putting the same care into the details and construction as J. Press, and that is evident just from looking at it.

But you're also asking a different question, it seems like. Is a Clipper Craft jacket from 1960 "better quality" than a Jos. A Bank jacket today, for example? I have no idea. My guess would be yes, but not by too much. The real advantage is just in the styling. The big change in men's clothing is that cheap suits today aren't worth the hanger they're sold on, and neither are good suits necessarily worth the bank vault they cost. Because of the fact that nearly everyone (at least in urban areas) needed to wear a certain baseline of formal clothing every day in the 50s and early 60s, there was a much wider range of available options, at a much wider variety of price points. Today, a cheap suit needs to last the one job interview it's bought for, rather than needing to be the equivalent of a J. Press suit in terms of times worn, but for a very different rung on the social ladder.

I had a Clipper Craft sport coat once upon a time, when I was less, er, robust. It was on a par with Corbin or Huntington, seemed to me. Nothing exceptional but it fit and looked right. If I was still 170 pounds I'd probably still be wearing it. But I'm not.

not a fan of Oxxford, don't think it's too Ivy or prep, more like Midwest Trad to me

Good point,Tom. A major difference between the American look as defined by Brooks Brothers and J. Press was, of course, that everything was off the rack, at least in theory.