This discussion feels informative rather than argumentative, please continue to discuss!
My plague-project has been restoring an '84 Olson 25. The first O25 I looked at had a foredeck that felt like it belonged on a Hobie Cat - the pulpit support pads are too small and easily puncture the foredeck in a collision. And these boats were and are raced aggressively on the SF Bay, so plenty of collisions in their history. My own boat had a number of different adhesives and sealants jammed into the damaged area under the pulpit supports. I took everything except the winches and mast off, inspected the balsa in every hole and found dry blonde wood. I then filled the holes with penetrating epoxy before drilling them out again and refitting all the deck hardware. Perhaps unnecessary, but this O25 should have another good 35 years racing on the bay if future owners take good care.
Before buying the O25, I had briefly considered a J/105 with significant soggy core issues. I can't tell you how lucky I am that I passed on that mess.
My boat significantly exceeded hull speed on the first day out, under dacron main & 95% jib. While I may have overdone the desk restoration, the performance of the boat made it absolutely worth it for me and future owners.
Foam cores seem like a nice improvement given the chronic issues that J/Boats seem to have with soggy balsa, but I'm surprised that they weren't able to improve their balsa process over all this time. I don't know if I'll be in the market for a J/45 or something more like a JPK when I'm ready to move on from the Olson. That may depend on how many years this plague remains active.
I hope you have a happy, safe, and healthy winter holiday as well!