Oliver Cowdery initially wrote & saith here in 𝓟; then somewhat later he inserted the subject pronoun he with slightly heavier ink flow. Perhaps Oliver’s correction was almost immediate, the result of him redipping his quill during his original copying. Or this change could represent Oliver’s proofing of 𝓟 against 𝓞 or perhaps even editing on his part. Elsewhere in the Book of Mormon text there are a number of places where a subject’s state of mind (of joy, anger, astonishment, sorrow, or peace of mind) is referred to, followed immediately by simply “and saith/said”, without any expressed subject:
There are two examples where the subject is repeated; for both of these examples, the subject is the plural pronoun they (in contrast to all the other examples, which have singular subjects):
Interestingly, in the first example (Alma 27:4) the 1841 British edition accidentally omitted the repeated they (thus giving “they were moved with compassion and said unto the king … ”). All in all, the many examples without any pronominal repetition of a singular subject argue that there is nothing wrong with having “and saith” in Mosiah 11:27. Nor has there been any tendency to supply the repeated subject for such examples. Thus the supralinearly inserted he in Mosiah 11:27 undoubtedly represents the original reading rather than the result of editing; the corrected reading in 𝓟 may have been added either as Oliver first copied from 𝓞 into 𝓟 or later when he proofed 𝓟 against 𝓞.
Summary: Retain in Mosiah 11:27 the repeated pronominal subject (“he was also wroth and he saith … ”) despite the relative infrequency of this construction in the text.