DC-AC losses are small (<5% I think), and the majority of solar systems aren't connected to storage at the moment.

Google ran a prize project to build a better inverter a while ago: https://blog.google/topics/environment/and-winner-of-1-milli...

"It had to have an efficiency greater than 95 percent and handle loads of 2 kVA. It also had to fit in a metal enclosure of no more than 40 cubic inches."

No - because 2.7% (or 0.7 efficiency difference) increase is not insignificant when you scale up. As an analogy, think of what 0.7% tax saving would mean to you annually.

In reality solar-cells and batteries are not at all cheap to install and maintain. We can scale up the solar cells and collect more energy. However, that needs more surface area to be covered with these panels. We still need better ways to store the energy efficiently.

Storing huge amounts of energy is easy: use pumps to add potential energy to water.

This isn't ultra efficient, but it's cheap and probably good enough. We have lots of experience with hydroelectric power.