(I’m not sure what portion of leaf blower noise is caused by the fan vs. the engine. I suspect even if the fan creates the larger component, it’s probably less annoying than the buzz of a two stroke engine).
EDIT: At the moment, I think gas powered units are still more powerful. But with battery technology going the way it is, and prices falling, I’d be surprised if a backpack electric unit doesn’t become cheap enough to rival current gas units. And even with some reduced power, users may prefer it to having to mix oil and maintain the units.