Well, I suppose so, but that's a matter of definitions. The real point is that the Trilemma's presentation of "lunatic" is of somebody who you cannot fail to notice is barking mad in any interaction with them (since the Trilemma's argument is that because Jesus was not obviously barking mad in that sense, he cannot have been a lunatic and hence was either genuine or deliberately lying), and I don't think it's immediately obvious that someone believing themselves to be the son of God must be totally incapable of normal function in all other areas as well.

(In addition, I can't help wondering whether the existence of prophecies about the Messiah might lead plenty of people to think "It Could Be You" sorts of thoughts; someone who actually did fulfill all the specified criteria might consider the possibility of messiah-hood to be a reasonable consequence of their existing belief in the prophecy, and if we posit the non-lunacy of the latter belief then jumping from "maybe I'm the messiah" to "actually I think I am" looks like rather less of a leap. Still not one I'd want to make myself without a very good reason, but.)

I think I agree... the analogy is simplistic and so isn't watertight. But even limited lunacy is still lunacy. Look at cult leaders such as David Koresh: cults grow because they appear plausible to their recruits (perhaps with some manipulation) but having seen what happened we'd still consider them fruitcakes rather than just a bit dappy. If they were raving to start with people wouldn't be taken in.

I suppose the questions to ask really are: a) are the New Testament accounts reliable and b) did they really happen? Because it's one thing to claim to be the Messiah but quite another to do things only the Messiah was capable of doing.