Here in the printer’s manuscript, Oliver Cowdery initially made two errors as he copied from 𝓞 into 𝓟. He initially wrote corrupt but later corrected it to corrupted by supralinearly inserting the -ed ending. And he initially skipped the word like, which he also later supralinearly inserted in 𝓟. For both corrections, the level of ink flow is somewhat heavier, which argues that both these corrections were made at the same time, apparently when Oliver proofed 𝓟 against 𝓞.
The like is necessary here. The text really makes no sense without the like, and 𝓞 undoubtedly had the word. For further discussion regarding the phrase “like (un)to X”, which occurred 89 times in the original text, see under Jacob 2:17.
Most likely, 𝓞 read corrupted. Note first of all that the use of corrupted here in Helaman 4:22 can be supported by the parallel language in nearby Helaman 5:2: “for the laws had become corrupted”. More generally, the text allows for either corrupt or corrupted as a predicate adjective, although most instances read corrupted (below I mark each case of corrupt with an asterisk):
Note that all three instances of corrupt occur in the allegory of the olive tree (in Jacob 5). Moreover, some passages show that basically the same phraseology can read with either corrupt or corrupted (compare, for instance, the two examples in Jacob 5:75). So in each case of predicate adjective corrupt(ed), the critical text will follow the earliest textual sources. It appears that here in Helaman 4:22 Oliver Cowdery would not have made the change to corrupted in 𝓟 unless 𝓞 read that way.
Summary: Accept Oliver Cowdery’s corrupted in Helaman 4:22, his corrected reading in 𝓟, as the reading of the original text; also accept the inserted like in 𝓟 (“like unto the Lamanites”), a correction also made at the same time that corrupt was corrected to corrupted.