We are forgetting, that Harry is not actually "good" at quick-magic (he cheats via stupendous brute forcing of magic juice with his tremendous power reserves and physical stamina), and especially not large scale or complex ones, like controlling the various "systems" incorporated into Merlin's tower seems to require. So I think it is actually possible for a single wizard to operate all the defenses, if they're good at that sort of thing. I would expect that it does not even have to be a spirit of intellect specifically, that would be required to be a stand-in for such skills, either, e.g. perhaps someone/something like the gargoyles may be able to do it too, or at least specific parts of it. And potentially, he could perhaps achieve the same level of control of those systems Bob has, but he'd need a bit of prep time for a more "serious" ritual to temporarily connect to them more directly, since with the battle at the end he only had like half an hour's worth of warning?
