Swinging a massive arm in Lancelot's direction was no more effective than simply striking out at him with human proportions;  the knight neatly jumped over what may as well have been a ponderously slow attack and cut into an elbow on the down-swing--though, obviously, the damage that one such as he could inflict immediately on such an enormous magical construct was quite limited. Perhaps the full release of his Noble Phantasm would be able to blast it apart... Excalibur would almost certainly do so. 

But if it was made entirely of magic, would it just restore itself from nothing? If something else was forcing it into existence, then an entirely new form could be constructed immediately--this, too, was Laetitia's thoughts, effectively prodding it with minor spells, almost tickling it, that served no purpose but to get an idea of what logic was [i]behind[/i] it. Where was the mana coming from, and could it be blocked off? Was this a projection of some sort from the bounded field? Or was it just a very large, shaky facsimile of a Servant that would go boom as easily (or more) as one of them?