The main advantage of AC, is that it was easier to step from one voltage to another using transformers, a technology from the 1800s. With modern solid state DC to DC converters, that is no longer an issue.
Do you know what the most efficient switch is for voltages over a kilovolt? I'll give you a hint: it's not based on semiconductors. Especially for high power. There's this little matter of "breakdown voltage," for one. Also "channel resistance." When someone comes up with a transistor  that can do three-nines  voltage conversion, we can talk.
 And bear in mind that I spent forty years making a good living from the little darlin's. I just don't hold illusions about 'em.
 Check the losses that power-station transformers tolerate while doing conversions on megawatts. Those suckers get effficient.