I believe it is a part of the issue. Getting to 2nd level may not matter much but third is a big factor. At 36 strength you also can begin to hit income buildings on the way and combined with the extra xp it matters. Other issue is all the extra powers sorceress can buy, and does do to all the leveling. She becomes a combo hero taking ruins and cities at too high a rate in the early game.
also note max strength is 40, not 45. those 45 strength sorceresses you see have been to a strength temple.