A similar alternative is the --strategy-option (short form -X) option, which accepts theirs. For example:
git checkout branchA
git merge -X theirs branchB
However, this is more equivalent to -X ours than -s ours. The key difference being that -X performs a regular recursive merge, resolving any conflicts using the chosen side, whereas -s ours changes the merge to just completely ignore the other side.
In some cases, the main problem using -X theirs instead of the hypothetical -s theirs is deleted files. In this case, just run git rm with the name of any files that were deleted:
git rm {DELETED-FILE-NAME}
After that, the -X theirs may work as expected.
Of course, doing the actual removal with the git rm command will prevent the conflict from happening in the first place.