As discussed under Alma 43:24, the original text frequently preferred the periphrastic forms for comparison of adjectives rather than the inflectional forms. Here in Alma 49:20, we have an instance of most strong that was changed to strongest in the 1920 LDS edition. In each case, the critical text will accept the comparative form found in the earliest textual sources.
Summary: Restore in Alma 49:20 the periphrastic form most strong; current English prefers the inflectional form strongest.