Yes, must be mainly that: labour cost + efficiency improvement (I think they said efficiency improved 80% over last 7 years; can't check because the website is down?). Impressive.

What I hope is that early adopters are not penalised so much by this fact. Ie. that panels are easily swappable (scaffolding and the rest can stay as is; maybe batteries need to be swapped) and there will be marked for old, less efficient panels (and used batteries?) to be sold to late adopters or subsidised recycling?

It is cost efficiency that has improved dramatically in the last 7 years, not device efficiency. Maybe 7 years ago you bought a module with a 14% sunlight-to-electricity conversion efficiency and today the same manufacturer would have a 16% efficient panel in the same part of their lineup. That is not a dramatic change. It's certainly not worth the cost of replacing panels that work just fine with this year's model.

You'd pay 75% less per watt of panel capacity today compared to 7 years ago, due to manufacturing improvements up and down the supply chain plus brutal market competition between manufacturers. That is a dramatic change.