Here in his editing for the 1837 edition, Joseph Smith replaced have fought with fight, although there seems to be nothing wrong here with the original use of the perfect have fought. A nearly parallel instance of this usage is found later in the book of Alma, but in that instance Joseph did not remove the perfective infinitive: “yea never was men known to have fought with such miraculous strength” (Alma 56:56). Perhaps the difference is that here in Alma 43:43 the main clause already has a perfective verb phrase (“never had the Lamanites been known to …”). In any event, the critical text will restore the original text in Alma 43:43; there is nothing wrong with this usage.
Summary: Restore in Alma 43:43 the original reading with its perfect infinitive: “never had the Lamanites been known to have fought with such exceeding great strength and courage”.