You can see even at utility scale the panel prices are generally less than 50%. I think 2018 increase was tariff related. Been out of the industry ~5 years so don't follow stuff that closely. Many of the other costs are basically a multiple of # of panels which would be 10x at 2% efficiency.
And that was the point - weight and difficulty of transporting the final system is a very important variable. Probably more important than efficiency when orders of magnitude are concerned. From a 25% base efficiency can double and double then it stops improving. Weights and installation costs due to the panel technology can halve and halve and halve and so on - and each halving reduces the cost of transporting the panels. There are more gains to be made there. It would be worth trading efficiency away to make big gains there.