The game came down to being a Big Gun tooting player.
Cmon, everyone knows there were speech options to get through the final part as well.
And there were plenty of people to snipe before getting to the Legate. Why couldn't you snope him as well, you have that option before the dialogue starts.
Also do you think someone who focus on science the whole games say "WTF? I couldn't
science my way out of the final boss? What gives?"