Efficiency gains are great, but the bigger gains are to be had in manufacturing, installation, and overhead costs. If we’re just talking residential, companies spend a couple thousand in customer acquisition costs per installation. The utility scale stuff is MUCH cheaper per kW, but can still wring out some more savings in siting, permitting, interconnection, and overheads. Panel efficiency gains tend to help more when space is more of a concern. If you can spread out, then much cheaper, less efficient panels are often the better choice.