…and BTW, the Rambam in Melachim u’Melchamos 7:4 does not specify that a Talmid Chacham is obligated to go to milchemes mitzva, only that those who are normally pattur from a milchemes reshus (such as a chosson, somebody who just bought a field, or somebody who’s just scared) are.
Therefore, this Rambam does not contradict the one in Hilchos Talmud Torah 6:10 that says that a Talmid Chacham is pattur from contributing towards the city’s defense, as does the Shulchan Oruch I quoted in the previous post (who adds that the reason is because their Torah protects).