I would guess that he was down-playing the difference to fit the discussion, whether that was to express confidence in a player's ability to play either or defend decisions made on putting players in a position.
I definitely would argue the statement on it's own - huge difference in ease of reading balls off the bat. RF almost always gets a slice/fade that is fairly easy to pick up. LF often gets pulls or hard hooks or liners straight at that can be very difficult to read. More balls that are hit deep stay in play and can be tracked down in RF, therefore a bit more speed is helpful. Deep balls to LF tend to leave the park or bounce hard of the fence. And, definitely agree with the arm strength issue.