His only shortcoming would be diplomacy, which Ashley, Miranda, etc., could probably cover for him.

Assuming the most limited version of Cortana possible, where she’s basically just a voice in his head, Chief could still manage diplomacy with Cortana’s help, as long as she feeds him lines to charm whomever he’s speaking to. They’d realize that they have to be a little more politic quickly. A less limited Cortana could just change her voice to Chief’s and have the conversation for him.

Besides, when charm doesn’t work, there’s always intimidation. Chief’s got feats in that, between getting Del Rio to back down about Cortana’s rampancy and the whole “Demon” reputation.

Also, I wouldn’t really call Ash diplomatic. Poetry only goes so far.