>liquid-CO2 system has a round-trip efficiency of 75-80%

You mean this part?

Edit: this is pretty much theoretical Carno cycle and it has moving parts

I think even 60% efficiency would still be fine if the storage was cheap enough and scales well. Just build more solar cells or wind mills to compensate the inefficiency. Neither lithium-ion nor gravity based systems seem particularly scalable to me. So a good-enough system that’s scalable will be a winner in the long run I think.

That's for heat conversion, no? This isn't about heat.