Sigh. I knew it was only a matter of time before this appeared here.

The author fails to recognize that Vader's chief goal was prisoners, Skywalker if possible. With this in mind, he can no longer use an aerial bombardment. Unfortunately, until that shield is down, he can't land sufficient numbers of troops required to clear out a rats-nest of caverns anywhere near the base, but the shield restricts him to walkers (or, I guess, tanks?) for moving big enough guns within range of the shield. Echo Base seems to have sufficient surveillance in place that a strike force (ala Endor) would have been futile (particularly with the climate making things...difficult), so a blazen frontal assault is a fine way to take out the shield.