Here the and was omitted in the 1874 RLDS edition; its loss was probably accidental. The 1908 RLDS edition restored the and to the RLDS text. There are four other instances in the text of “yea and that S”, where S is a finite clause. For a list, see the discussion regarding “yea and that S” under Alma 36:13–14. In these other cases, there is a preceding that-clause that the yea-clause refers to. Here in Helaman 7:21, on the other hand, the preceding clause is infinitival rather than being a that-clause (“to get gain / to be praised of men”).
As we might expect, there are examples in the text of “yea that S”—that is, without an intervening and. Of the seven instances of “yea that S”, five of them refer to a preceding that-clause. But in two cases the preceding conjoined text is not a subordinate that-clause:
Thus there is nothing wrong in Helaman 7:21 with having “yea and that S” refer to a preceding infinitival clause (“to get gain / to be praised of men”) rather than to a more expected that-clause.
Summary: Accept in Helaman 7:21 the use of the and in the yea-clause, the reading of the earliest extant source, the printer’s manuscript.