I agree that the wisdom is questionable when referring to this whole ordeal in terms of a nine-on-nine slaughterfest o'rama-thon. However, none of the nine walkers were chosen solely for how much of a can o' whoop-arse they could open in a skirmish.

The Fellowship's strength and ally was supposed to be stealth. They argued all the while about who would end up going with Frodo once they got to the Ephel Duath, none of them truly believed they would storm the Black Gate in unison.

Legolas went along to represent his people, as we know, but Sauron was truly not the elves problem anymore. They had already suffered innumerable losses at his-and Morgoth's-hands, and sending Glorfindel was just not an option any more. It was man's great battle, clearly, and the elves knew that they aided Frodo's great task at their own peril. Although I do agree that one more walker, especially of the caliber of Glorfindel, could have been reasonable.