I don't wear sweaters around my neck, but I'm not sure that's a fair comparison. Suit and sport coats are not intended to keep one warm (generally). If that were the case, I would never wear a suit or sport coat, given where I live. Different story with sweaters.
Of course it's a fair comparison.
Nobody has asserted that adopting the sweater noose has anything to do with the fact that the garment is intended to keep one warm, but rather that variance in temperature during wear necessitates this particular response.
I find that a bit hard to swallow.
A sport coat could just as easily be the smart casual choice on a cool fall morning that sees warming temperatures throughout the day, followed by a return to cooler temps in the evening. The reason nobody would loop the sport coat around the neck during the warmer hours is that it would look absolutely ridiculous. And they would somehow manage to deal carrying said sport coat if it in fact proved to be to unbearable to wear.
Doing so with a sweater also looks ridiculous, but it was a preppy affectation in the '80s that some thought was awesome then (and was manifestly NOT undertaken for any practical reason) and still think is awesome now. If you like the look, rock it all day long. But the claim that it is the only practical way to deal with temperature change is a bit precious.
By the way - I categorically reject your assertion that sport coats are not intended to keep one warm. There is a reason some are made in linen, while others are made in heavy wool, tweed and cashmere