Welcome to Lexus Enthusiast, Sprat
One must remember that the GX, a body-on-frame/truck-derived SUV, shares its platform with the Toyota 4Runner and Prado, and is not designed for the same purpose, or the same driving conditions, as a BMW X5.
In the Lexus family, a somewhat closer comparison to the BMW X5, platform/chassis-wise, would probably be the RX350 F-Sport....though the X5, at 445 HP, definitely has a stronger top-level power plant.