Not sure a late molt indicates any meteorological intuition.....
.....or they'd have had all their new feathers grown in by now, eh?
"Heavy" (did you mean hard molt ?) just means they lose all their feathers fast rather than slowly...and that I think depends on the individual bird or maybe nutritional aspects.
Most all adult birds replace all their feathers every year..they don't grow extra long ones for a heavier 'coat' like mammals can.
So it's pretty basic. As early as October I noticed that there were many more feathers in the run and coop this year over previous years. My chickens don't drop all of their feathers at once, nor ever appear "bald" at any given time. The molt has always been long enough to drop and regrow so that they are never bald. I only raise Buff Orpingtons, a heritage breed that has been outdoor raised since the 1800's. But this year there were more feathers dropped during the molt than normal.
I am calling that a "hard or heavy molt", not a technical term just using it to express a meaning.
Now you might say that if a bird losses a specific amount of feathers in a given year then there would in reality be no more or less feathers dropped in a given molt but I am not so sure about that.
Chickens loose some feathers all year. I know this because all year I find some feathers here and there, some are pulled out in "disagreements" with others in the flock, some are pulled by the hen herself to make bedding, etc. But some just fall out at various times of the year. I know this because if I pick up my hen and pet her in a non-molt season and I might get a feather or two on my hands.
So what would a "hard or heavy molt" mean in terms of a hen preparing for winter? Perhaps she sheds more of those feather during the molt: all of the ones she would normally shed in a light molt, plus go ahead and drop whatever feathers she would have lost naturally after the molt, in say Jan, Feb, March & April and maximize the feather count going through those months. I don't know - theory, not necessarily scientifically proven. Maybe it is to produce thicker shafts, or denser plumage.
There was a second part to this molt season that seemed to add further evidence. The egg production also dropped well below a normal molt, given the same ration. Now this tells me that even more protein was needed to cover one of two things: either the making of more feathers than normal and/or the making of denser/fluffier feathers. Again, I don't know - just theory.
But I will say that the majority of the response (85%?) that I have received on this subject in the original Facebook group post, which is local to my area, all agreed that this was a hard molt year, that more feathers than normal dropped, and egg production was much lower. I was interested to see what the responses would be here as it gathers input from across the country and Canada.
It may be that there is nothing to it, but it is hard to ignore the very real evidence.