Consider that a first-order crossover with 10dB padding is -16dB an octave below crossover. The same thing but with a third-order filter is -28dB one octave below. The tweeter with the third-order filter is receiving less energy one octave below crossover (-18dB) than the first-order filter (-6dB), even if the first-order solution is padded 10x (-16dB).

It's not that the first-order solution is without merit. It's just that you can't hit the dynamic range peaks with a compression tweeter using a first-order crossover as you can with a higher-order slope.