The practical limit for an ICE engine in a road car (in a hybrid configuration) is probably somewhere in the neighborhood of 50% (small sizes make efficiency harder). A theoretical ideal ICE hybrid would almost certainly beat a current day EV on the current day grid. But that's not a fair comparison, and we have to modernize the grid anyway.

F1 PUs are absolutely designed with efficiency in mind. The FIA limits both the maximum fuel used in a race, as well as the instantaneous fuel flow rate. When fuel flow rates are capped, getting more power is the same thing as getting more efficiency.