At 12U we teach our RF to make the throw to 3rd without a relay if they are charging a ground ball. In HS, it should be a no brainer.
There still should be an interior cut-off even if you are throwing directly to 3B because sometimes in that situation if runner is fast enough, was stealing on pitch etc... you want to cut the ball in the infield for a chance to make a play on the batter trying for 2B.
I've always had very good fielding pitchers and I always had them be the interior cut, our HS coach uses F3 for all interior cuts (not a big fan of that because that begs batter in this sich to round hard and evaluate their options with no chance to get them at 1B once F3 vacates.)